Activated microglia/macrophage whey acidic protein (AMWAP) inhibits NFκB signaling and induces a neuroprotective phenotype in microglia

Nattokinase's Neuroprotective Mechanisms in Ischemic Stroke: Targeting Inflammation, Oxidative Stress, and Coagulation

Aims: Nattokinase (NK), a potent serine endopeptidase, has exhibited a variety of pharmacological effects, including thrombolysis, anti-inflammation, and antioxidative stress. Building on previous research highlighting NK's promise in nerve regeneration, our study investigated whether NK exerted protective effects in transient middle cerebral artery occlusion (tMCAO)-induced cerebral ischemia-reperfusion injury and the underlying mechanisms. Results: The rats were administered NK (5000, 10000, 20000 FU/kg, i.g., 7 days before surgery, once daily). We showed that NK treatment dose dependently reduced the infarction volume and improved neurological symptoms, decreased the proinflammatory and coagulation cytokines levels, and attenuated reactive oxygen species (ROS) in the infarcted area of tMCAO rats. We also found that NK could exert neuroprotective effects in a variety of vitro models, including the microglia inflammation model and neuronal oxygen-glucose deprivation/reperfusion (OGD/R) model. Notably, NK effectively countered OGD/R-induced neuron death, modulating diverse pathways, including autophagy, apoptosis, PARP-dependent death, and endoplasmic reticulum stress. Furthermore, the neuroprotection of NK was blocked by phenylmethylsulfonyl fluoride (PMSF), a serine endopeptidase inhibitor. We revealed that heat-inactive NK was unable to protect against tMCAO injury and other vitro models, suggesting NK attenuated ischemic injury by its enzymatic activity. We conducted a proteomic analysis and found inflammation and coagulation were involved in the occurrence of tMCAO model and in the therapeutic effect of NK. Innovation and Conclusion: In conclusion, these data demonstrated that NK had multifaceted neuroprotection in ischemic brain injury, and the therapeutic effect of NK was related with serine endopeptidase activity.

Chronic social defeat stress induces meningeal neutrophilia via type I interferon signaling

Animal models of stress and stress-related disorders are also associated with blood neutrophilia. The mechanistic relevance of this to symptoms or behavior is unclear. We used cytometry, immunohistochemistry, whole tissue clearing, and single-cell sequencing to characterize the meningeal immune response to chronic social defeat (CSD) stress in mice. We find that chronic, but not acute, stress causes meningeal neutrophil accumulation, and CSD increases neutrophil trafficking in vascular channels emanating from skull bone marrow (BM). Transcriptional analysis suggested CSD increases type I interferon (IFN-I) signaling in meningeal neutrophils. Blocking this pathway via the IFN-I receptor (IFNAR) protected against the anhedonic and anxiogenic effects of CSD stress, potentially through reduced infiltration of IFNAR+ neutrophils into the meninges from skull BM. Our identification of IFN-I signaling as a putative mediator of meningeal neutrophil recruitment may facilitate development of new therapies for stress-related disorders.

Inflammation is a critical factor for successful regeneration of the adult zebrafish retina in response to diffuse light lesion

Inflammation can lead to persistent and irreversible loss of retinal neurons and photoreceptors in mammalian vertebrates. In contrast, in the adult zebrafish brain, acute neural inflammation is both necessary and sufficient to stimulate regeneration of neurons. Here, we report on the critical, positive role of the immune system to support retina regeneration in adult zebrafish. After sterile ablation of photoreceptors by phototoxicity, we find rapid response of immune cells, especially monocytes/microglia and neutrophils, which returns to homeostatic levels within 14 days post lesion. Pharmacological or genetic impairment of the immune system results in a reduced Müller glia stem cell response, seen as decreased reactive proliferation, and a strikingly reduced number of regenerated cells from them, including photoreceptors. Conversely, injection of the immune stimulators flagellin, zymosan, or M-CSF into the vitreous of the eye, leads to a robust proliferation response and the upregulation of regeneration-associated marker genes in Müller glia. Our results suggest that neuroinflammation is a necessary and sufficient driver for retinal regeneration in the adult zebrafish retina.

Single-Cell RNA Sequencing Reveals Immunomodulatory Effects of Stem Cell Factor and Granulocyte Colony-Stimulating Factor Treatment in the Brains of Aged APP/PS1 Mice

Alzheimer's disease (AD) leads to progressive neurodegeneration and dementia. AD primarily affects older adults with neuropathological changes including amyloid-beta (Aβ) deposition, neuroinflammation, and neurodegeneration. We have previously demonstrated that systemic treatment with combined stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF) (SCF+G-CSF) reduces the Aβ load, increases Aβ uptake by activated microglia and macrophages, reduces neuroinflammation, and restores dendrites and synapses in the brains of aged APPswe/PS1dE9 (APP/PS1) mice. However, the mechanisms underlying SCF+G-CSF-enhanced brain repair in aged APP/PS1 mice remain unclear. This study used a transcriptomic approach to identify the potential mechanisms by which SCF+G-CSF treatment modulates microglia and peripheral myeloid cells to mitigate AD pathology in the aged brain. After injections of SCF+G-CSF for 5 consecutive days, single-cell RNA sequencing was performed on CD11b+ cells isolated from the brains of 28-month-old APP/PS1 mice. The vast majority of cell clusters aligned with transcriptional profiles of microglia in various activation states. However, SCF+G-CSF treatment dramatically increased a cell population showing upregulation of marker genes related to peripheral myeloid cells. Flow cytometry data also revealed an SCF+G-CSF-induced increase of cerebral CD45high/CD11b+ active phagocytes. SCF+G-CSF treatment robustly increased the transcription of genes implicated in immune cell activation, including gene sets that regulate inflammatory processes and cell migration. The expression of S100a8 and S100a9 was robustly enhanced following SCF+G-CSF treatment in all CD11b+ cell clusters. Moreover, the topmost genes differentially expressed with SCF+G-CSF treatment were largely upregulated in S100a8/9-positive cells, suggesting a well-conserved transcriptional profile related to SCF+G-CSF treatment in resident and peripherally derived CD11b+ immune cells. This S100a8/9-associated transcriptional profile contained notable genes related to pro-inflammatory and anti-inflammatory responses, neuroprotection, and Aβ plaque inhibition or clearance. Altogether, this study reveals the immunomodulatory effects of SCF+G-CSF treatment in the aged brain with AD pathology, which will guide future studies to further uncover the therapeutic mechanisms.

Anatomical location of injected microglia in different activation states and time course of injury determines survival of retinal ganglion cells after optic nerve crush

Background: Activated microglia release harmful substances to retinal ganglion cells (RGCs), but may also benefit by removing cellular debris and secreting neurotrophic factors. These paradoxical roles remain controversial because the nature and time-course of the injury that defines their role is unknown. The aim of this study was to determine if pharmacological manipulation of microglia to acquire a pro-inflammatory or pro-survival phenotype will exacerbate or enhance neuronal survival after injury.Material and methods: Treated HAP I (highly aggressively proliferating immortalized) microglia were injected into the vitreous or tail vein (T V) of female Sprague-Dawley rats. Retinas were examined at 4-14 days following optic nerve crush (ONC) and the number of surviving RGCs was determined.Results: Injection of untreated HAP I cells resulted in the greater loss of RGCs early after ONC when injected into the vitreous and later after ONC when injected into the T V. LP S activated HAP I cells injected into the vitreous resulted in greater RGC loss with and without injury. When injected into the T V with ONC there was no loss of RGCs 4 days after ONC but greater loss afterwards. Minocycline treated HAP I cells injected into the vitreous resulted in greater RGC survival than untreated HAP I cells. However, when injected into the T V with ONC there was greater loss of RGCs. These results suggest that optic nerve signals attract extrinsic microglia to the retina, resulting in a proinflammatory response.Conclusion: Neuroprotection or cytotoxicity of microglia depends on the type of activation, time course of the injury, and if they act on the axon or cell body.

Single cell RNA sequencing reveals immunomodulatory effects of stem cell factor and granulocyte colony-stimulating factor treatment in the brains of aged APP/PS1 mice

Alzheimers disease leads to progressive neurodegeneration and dementia. Alzheimers disease primarily affects older adults with neuropathological changes including amyloid beta deposition, neuroinflammation, and neurodegeneration. We have previously demonstrated that systemic treatment with combined stem cell factor, SCF, and granulocyte colony stimulating factor, GCSF, reduces amyloid beta load, increases amyloid beta uptake by activated microglia and macrophages, reduces neuroinflammation, and restores dendrites and synapses in the brains of aged APP-PS1 mice. However, the mechanisms underlying SCF-GCSF-enhanced brain repair in aged APP-PS1 mice remain unclear. This study used a transcriptomic approach to identify potential mechanisms by which SCF-GCSF treatment modulates microglia and peripheral myeloid cells to mitigate Alzheimers disease pathology in the aged brain. After injections of SCF-GCSF for 5 consecutive days, single cell RNA sequencing was performed on CD11b positive cells isolated from the brains of 28-month-old APP-PS1 mice. The vast majority of cell clusters aligned with transcriptional profiles of microglia in various activation states. However, SCF-GCSF treatment dramatically increased a cell population showing upregulation of marker genes related to peripheral myeloid cells. Flow cytometry data also revealed an SCF-GCSF-induced increase of cerebral CD45high-CD11b positive active phagocytes. SCF-GCSF treatment robustly increased the transcription of genes implicated in immune cell activation, including gene sets that regulate inflammatory processes and cell migration. Expression of S100a8 and S100a9 were robustly enhanced following SCF-GCSF treatment in all CD11b positive cell clusters. Moreover, the topmost genes differentially expressed with SCF-GCSF treatment were largely upregulated in S100a8-S100a9 positive cells, suggesting a well-conserved transcriptional profile related to SCF-GCSF treatment in resident and peripherally derived CD11b positive immune cells. This S100a8-S100a9-associated transcriptional profile contained notable genes related to proinflammatory and antiinflammatory responses, neuroprotection, and amyloid beta plaque inhibition or clearance. Altogether, this study reveals immunomodulatory effects of SCF-GCSF treatment in the aged brain with Alzheimers disease pathology, which will guide future studies to further uncover the therapeutic mechanisms.

Stimulation of the Pro-Resolving Receptor Fpr2 Reverses Inflammatory Microglial Activity by Suppressing NFκB Activity

Neuroinflammation driven primarily by microglia directly contributes to neuronal death in many neurodegenerative diseases. Classical anti-inflammatory approaches aim to suppress pro-inflammatory mediator production, but exploitation of inflammatory resolution may also be of benefit. A key driver of peripheral inflammatory resolution, formyl peptide receptor 2 (Fpr2), is expressed by microglia, but its therapeutic potential in neurodegeneration remains unclear. Here, we studied whether targeting of Fpr2 could reverse inflammatory microglial activation induced by the potent bacterial inflammogen lipopolysaccharide (LPS). Exposure of murine primary or immortalised BV2 microglia to LPS triggered pro-inflammatory phenotypic change and activation of ROS production, effects significantly attenuated by subsequent treatment with the Fpr2 agonist C43. Mechanistic studies showed C43 to act through p38 MAPK phosphorylation and reduction of LPS-induced NFκB nuclear translocation via prevention of IκBα degradation. Here, we provide proof-of-concept data highlighting Fpr2 as a potential target for control of microglial pro-inflammatory activity, suggesting that it may be a promising therapeutic target for the treatment of neuroinflammatory disease.

Roflumilast attenuates neuroinflammation post retinal ischemia/reperfusion injury by regulating microglia phenotype via the Nrf2/STING/NF-κB pathway

PURPOSE

The abnormal polarisation of microglial cells (MGs) following retinal ischemia/reperfusion (RIR) initiates neuroinflammation and progressive death of retinal ganglion cells (RGCs), causing increasingly severe and irreversible visual dysfunction. Roflumilast (Roflu) is a promising candidate for treating neuroinflammatory diseases. This study aimed to explore whether Roflu displayed a cytoprotective effect against RIR-induced neuroinflammation and to characterise the underlying signalling pathway.

METHODS

The effects and mechanism of Roflu against RIR injury were investigated in C57BL/6J mice and the BV2 cell line. We used quantitative real-time PCR and enzyme-linked immunosorbent assay to examine the levels of inflammatory factors. Furthermore, haematoxylin and eosin and immunofluorescence (IF) stainings were used to assess the morphology of the retina and the states of MGs and RGCs. Reactive oxygen species (ROS) levels were examined using a ROS assay kit, while whole-genome sequencing analysis was conducted to identify altered pathways and molecules. Western blotting and IF staining were used to quantify the proteins associated with the nuclear factor erythroid 2-related factor 2 (Nrf2)/stimulator of interferon gene (STING)/nuclear factor kappa beta (NF-κB) pathway.

RESULTS

MG polarisation includes the pro-inflammatory and neurotoxic M1 phenotype as well as the anti-inflammatory and neuroprotective M2 phenotype. Roflu significantly attenuated MG activation and contributed to a shift in the MG phenotype from M1 to M2. Moreover, Roflu decreased ROS release and increased heme oxygenase 1 and NAD(P)H quinone oxidoreductase 1 expression. In vitro and in vivo experiments validated that Roflu exerted its neuroprotective effects primarily by upregulating the Nrf2/STING/NF-κB pathway. However, these effects were abrogated when the Nrf2 expression was inhibited by pharmacological or genetic manipulation.

CONCLUSIONS

Roflu suppressed RIR-induced neuroinflammation by driving the shift of MG polarisation from M1 to M2 phenotype, which was mediated by the upregulation of the Nrf2/STING/NK-κB pathway.

Pathological mechanisms of neuroimmune response and multitarget disease-modifying therapies of mesenchymal stem cells in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by the degeneration of dopaminergic neurons in the substantia nigra (SN); the etiology and pathological mechanism of the disease are still unclear. Recent studies have shown that the activation of a neuroimmune response plays a key role in the development of PD. Alpha-synuclein (α-Syn), the primary pathological marker of PD, can gather in the SN and trigger a neuroinflammatory response by activating microglia which can further activate the dopaminergic neuron's neuroimmune response mediated by reactive T cells through antigen presentation. It has been shown that adaptive immunity and antigen presentation processes are involved in the process of PD and further research on the neuroimmune response mechanism may open new methods for its prevention and therapy. While current therapeutic regimens are still focused on controlling clinical symptoms, applications such as immunoregulatory strategies can delay the symptoms and the process of neurodegeneration. In this review, we summarized the progression of the neuroimmune response in PD based on recent studies and focused on the use of mesenchymal stem cell (MSC) therapy and challenges as a strategy of disease-modifying therapy with multiple targets.

Gene Expression Profile in the Sandhoff Mouse Brain with Progression of Age

Sandhoff disease (SD) is a fatal neurodegenerative disorder belonging to the family of diseases called GM2 Gangliosidosis. There is no curative treatment of SD. The molecular pathogenesis of SD is still unclear though it is clear that the pathology initiates with the build-up of ganglioside followed by microglial activation, inflammation, demyelination and apoptosis, leading to massive neuronal loss. In this article, we explored the expression profile of selected immune and myelination associated transcripts (Wfdc17, Ccl3, Lyz2, Fa2h, Mog and Ugt8a) at 5-, 10- and 16-weeks, representing young, pre-symptomatic and late stages of the SD mice. We found that immune system related genes (Wfdc17, Ccl3, Lyz2) are significantly upregulated by several fold at all ages in Hexb-KO mice relative to Hexb-het mice, while the difference in the expression levels of myelination related genes is not statistically significant. There is an age-dependent significant increase in expression of microglial/pro-inflammatory genes, from 5-weeks to the near humane end-point, i.e., 16-week time point; while the expression of those genes involved in myelination decreases slightly or remains unchanged. Future studies warrant use of new high-throughput gene expression modalities (such as 10X genomics) to delineate the underlying pathogenesis in SD by detecting gene expression changes in specific neuronal cell types and thus, paving the way for rational and precise therapeutic modalities.

Neuroinflammation in retinitis pigmentosa: Therapies targeting the innate immune system

Retinitis pigmentosa (RP) is an important cause of irreversible blindness worldwide and lacks effective treatment strategies. Although mutations are the primary cause of RP, research over the past decades has shown that neuroinflammation is an important cause of RP progression. Due to the abnormal activation of immunity, continuous sterile inflammation results in neuron loss and structural destruction. Therapies targeting inflammation have shown their potential to attenuate photoreceptor degeneration in preclinical models. Regardless of variations in genetic background, inflammatory modulation is emerging as an important role in the treatment of RP. We summarize the evidence for the role of inflammation in RP and mention therapeutic strategies where available, focusing on the modulation of innate immune signals, including TNFα signaling, TLR signaling, NLRP3 inflammasome activation, chemokine signaling and JAK/STAT signaling. In addition, we describe epigenetic regulation, the gut microbiome and herbal agents as prospective treatment strategies for RP in recent advances.

Microglia-mediated neuroinflammation and neuroplasticity after stroke

Stroke remains a major cause of long-term disability and mortality worldwide. The immune system plays an important role in determining the condition of the brain following stroke. As the resident innate immune cells of the central nervous system, microglia are the primary responders in a defense network covering the entire brain parenchyma, and exert various functions depending on dynamic communications with neurons, astrocytes, and other neighboring cells under both physiological or pathological conditions. Microglia activation and polarization is crucial for brain damage and repair following ischemic stroke, and is considered a double-edged sword for neurological recovery. Microglia can exist in pro-inflammatory states and promote secondary brain damage, but they can also secrete anti-inflammatory cytokines and neurotrophic factors and facilitate recovery following stroke. In this review, we focus on the role and mechanisms of microglia-mediated neuroinflammation and neuroplasticity after ischemia and relevant potential microglia-based interventions for stroke therapy.

Insulin-Like Growth Factor 1 Attenuates the Pro-Inflammatory Phenotype of Neutrophils in Myocardial Infarction

Acute myocardial infarction (MI) induces an extensive sterile inflammation, which is dominated in the early phase by invading neutrophils and monocytes/macrophages. The inflammatory response after MI critically affects infarct healing and cardiac remodeling. Therefore, modulation of cardiac inflammation may improve outcome post MI. Insulin-like growth factor 1 (IGF1) treatment reduces infarct size and improves cardiac function after MI via IGF1 receptor mediated signaling in myeloid cells. Our study aimed to investigate the effect of IGF1 on neutrophil phenotype both in vitro and in vivo after MI. We show that IGF1 induces an anti-inflammatory phenotype in bone marrow derived neutrophils. On the molecular and functional level IGF1 treated neutrophils were indistinguishable from those induced by IL4. Surprisingly, insulin, even though it is highly similar to IGF1 did not create anti-inflammatory neutrophils. Notably, the IGF1 effect was independent of the canonical Ras/Raf/ERK or PI3K/AKT pathway, but depended on activation of the JAK2/STAT6 pathway, which was not activated by insulin treatment. Single cell sequencing analysis 3 days after MI also showed that 3 day IGF1 treatment caused a downregulation of pro-inflammatory genes and upstream regulators in most neutrophil and many macrophage cell clusters whereas anti-inflammatory genes and upstream regulators were upregulated. Thus, IGF1 acts like an anti-inflammatory cytokine on myeloid cells in vitro and attenuates the pro-inflammatory phenotype of neutrophils and macrophages in vivo after MI. IGF1 treatment might therefore represent an effective immune modulatory therapy to improve the outcome after MI.

IL-17A in diabetic kidney disease: protection or damage

The effect of IL-17A in diabetic kidney disease (DKD) has received increasing attention. Interleukin (IL)-17A promotes renal inflammation and the progression of DKD, and IL-17A deficiency improves experimental DKD. However, recent studies have found that the effect of IL-17A on DKD is more complicated than the negative impact. IL-17A alleviates renal inflammation and fibrosis via regulating autophagy or the macrophage phenotype. Moreover, paradoxical expression of IL-17A has been reported in human DKD. This review focuses on how IL-17A affects the progression of DKD and the resulting opportunities and challenges.

Innate immune responses after stimulation with Toll-like receptor agonists in ex vivo microglial cultures and an in vivo model using mice with reduced microglia

Background

Past experiments studying innate immunity in the central nervous system (CNS) utilized microglia obtained from neonatal mouse brain, which differ developmentally from adult microglia. These differences might impact our current understanding of the role of microglia in CNS development, function, and disease.

Methods

Cytokine protein secretion was compared in ex vivo P3 and adult microglial cultures after exposure to agonists for three different toll-like receptors (TLR4, lipopolysaccharide [LPS]; TLR7, imiquimod [IMQ]; and TLR9, CpG Oligodeoxynucleotide [CpG-ODN] 1585). In addition, changes in inflammatory gene expression in ex vivo adult microglia in response to the TLR agonists was assessed. Furthermore, in vivo experiments evaluated changes in gene expression associated with inflammation and TLR signaling in brains of mice with or without treatment with PLX5622 to reduce microglia.

Results

Ex vivo adult and P3 microglia increased cytokine secretion when exposed to TLR4 agonist LPS and to TLR7 agonist IMQ. However, adult microglia decreased expression of numerous genes after exposure to TLR 9 agonist CpG-ODN 1585. In contrast, in vivo studies indicated a core group of inflammatory and TLR signaling genes increased when each of the TLR agonists was introduced into the CNS. Reducing microglia in the brain led to decreased expression of various inflammatory and TLR signaling genes. Mice with reduced microglia showed extreme impairment in upregulation of genes after exposure to TLR7 agonist IMQ.

Conclusions

Cultured adult microglia were more reactive than P3 microglia to LPS or IMQ exposure. In vivo results indicated microglial influences on neuroinflammation were agonist specific, with responses to TLR7 agonist IMQ more dysregulated in mice with reduced microglia. Thus, TLR7-mediated innate immune responses in the CNS appeared more dependent on the presence of microglia. Furthermore, partial responses to TLR4 and TLR9 agonists in mice with reduced microglia suggested other cell types in the CNS can compensate for their absence.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02240-w.

Key Role of Microglial Matrix Metalloproteinases in Choroidal Neovascularization

Age-related macular degeneration (AMD), especially neovascular AMD with choroidal neovascularization (CNV), is the leading cause of blindness in the elderly. Although matrix metalloproteinases (MMPs) are involved in pathological ocular angiogenesis, including CNV, the cellular origin of MMPs in AMD remains unknown. The present study investigated the role of microglial MMPs in CNV. MMP activities were analyzed by gelatin zymography in aqueous humor samples from patients with CNV and laser-induced CNV mice. Active MMP-9 was increased in the aqueous humor samples from neovascular AMD patients compared with control subjects. In the retinal pigment epithelium (RPE)/choroid from CNV mice, active MMP-9 increased, beginning 1 h post-CNV induction, and remained upregulated until Day 7. In RPE/choroid from CNV mice, active MMP-9 was suppressed by minocycline, a known microglial inhibitor, at 6 h and 1-day post-CNV induction. Flow cytometry revealed that the proportion of activated microglia increased very early, beginning at 1 h post-CNV induction, and was maintained until Day 7. Similarly, immunohistochemistry revealed increased microglial activation and MMP-9 expression on CNV lesions at 6 h and 1-day post-CNV induction. SB-3CT, an MMP inhibitor, decreased vascular leakage and lesion size in laser-induced CNV mice. These findings indicated nearly immediate recruitment of activated microglia and very early MMP-9 activation in the RPE/choroid. The present study newly identified a potential role for early microglial MMP-9 expression in CNV, and furthermore that modulating microglial MMP expression is a novel putative therapeutic for CNV.

Activated microglia-induced neuroinflammatory cytokines lead to photoreceptor apoptosis in Aβ-injected mice

Age-related macular degeneration (AMD) is mainly characterized by the progressive accumulation of drusen deposits and loss of photoreceptors and retinal pigment epithelial (RPE) cells. Because amyloid β (Aβ) is the main component of drusen, Aβ-induced activated microglia most likely lead to neuroinflammation and play a critical role in the pathogenesis of AMD. However, the relationship between activated microglia-mediated neuroinflammatory cytokines and photoreceptor death has not been clarified. By subretinal injection of Aβ₄₂ in mice, we mimicked an inflammatory milieu of AMD to better understand how activated microglia-induced neuroinflammatory cytokines lead to photoreceptor apoptosis in the AMD progression. We demonstrated that subretinal injection of Aβ₄₂ induces microglial activation and increases inflammatory cytokine release, which gives rise to photoreceptor apoptosis in mice. Our results were verified in vitro by co-culture of Aβ₄₂ activated primary microglia and the photoreceptor cell line 661W. We also demonstrated that the p38 mitogen-activated protein kinase (MAPK) signaling pathway was involved in Aβ₄₂-induced microglial activation and inflammatory cytokine release. Overall, our findings indicate that activated microglia-derived neuroinflammatory cytokines could contribute to photoreceptor apoptosis under the stimulation of Aβ₄₂. Moreover, this study may provide a potential therapeutic approach for AMD. KEY MESSAGES: Further explore the association between activated microglia-derived neuroinflammatory cytokine secretion and photoreceptor apoptosis under the stimulation of Aβ₄₂. Subretinal injection of Aβ₄₂ induces the activation of microglia and increases proinflammatory cytokines IL-1β and COX-2 expression in the retina, which could give rise to the deterioration of visual function and aggravate photoreceptor apoptosis in mice. Primary microglial are activated and the levels of proinflammatory cytokines are increased by Aβ₄₂ stimulation, which could increase the apoptosis of photoreceptor cell line 661W in vitro. The p38 MAPK signaling pathway is involved in microglial activation and photoreceptor apoptosis under Aβ₄₂ treatment.

Indole-3-carbinol regulates microglia homeostasis and protects the retina from degeneration

BACKGROUND

Retinal degenerative diseases significantly contribute to visual impairment and blindness. Microglia reactivity is a hallmark of neurodegenerative diseases including retinal cell death and immunomodulation emerges as a therapeutic option. Indole-3-carbinol (I3C) is a natural ligand of aryl hydrocarbon receptor (AhR), with potent immunomodulatory properties. Here, we hypothesized that I3C may inhibit microglia reactivity and exert neuroprotective effects in the light-damaged murine retina mimicking important immunological aspects of retinal degeneration.

METHODS

BV-2 microglia were treated in vitro with I3C followed by lipopolysaccharide (LPS) stimulation to analyze pro-inflammatory and anti-oxidant responses by quantitative real-time PCR (qRT-PCR) and Western blots. Nitric oxide (NO) secretion, caspase 3/7 levels, phagocytosis rates, migration, and morphology were analyzed in control and AhR knockdown cells. I3C or vehicle was systemically applied to light-treated BALB/cJ mice as an experimental model of retinal degeneration. Pro-inflammatory and anti-oxidant responses in the retina were examined by qRT-PCR, ELISA, and Western blots. Immunohistochemical staining of retinal flat mounts and cryosections were performed. The retinal thickness and structure were evaluated by in vivo imaging using spectral domain-optical coherence tomography (SD-OCT).

RESULTS

The in vitro data showed that I3C potently diminished LPS-induced pro-inflammatory gene expression of I-NOS, IL-1ß, NLRP3, IL-6, and CCL2 and induced anti-oxidants gene levels of NQO1, HMOX1, and CAT1 in BV-2 cells. I3C also reduced LPS-induced NO secretion, phagocytosis, and migration as important functional microglia parameters. siRNA-mediated knockdown of AhR partially prevented the previously observed gene regulatory events. The in vivo experiments revealed that I3C treatment diminished light-damage induced I-NOS, IL-1ß, NLRP3, IL-6, and CCL2 transcripts and also reduced CCL2, I-NOS, IL-1ß, p-NFkBp65 protein levels in mice. Moreover, I3C increased anti-oxidant NQO1 and HMOX1 protein levels in light-exposed retinas. Finally, I3C therapy prevented the accumulation of amoeboid microglia in the subretinal space and protected from retinal degeneration.

CONCLUSIONS

The AhR ligand I3C potently counter-acts microgliosis and light-induced retinal damage, highlighting a potential treatment concept for retinal degeneration.

Polysialic acid and Siglec-E orchestrate negative feedback regulation of microglia activation

Polysialic acid (polySia) emerges as a novel regulator of microglia activity. We recently identified polysialylated proteins in the Golgi compartment of murine microglia that are released in response to inflammatory stimulation. Since exogenously added polySia is able to attenuate the inflammatory response, we proposed that the release of polysialylated proteins constitutes a mechanism for negative feedback regulation of microglia activation. Here, we demonstrate that translocation of polySia from the Golgi to the cell surface can be induced by calcium depletion of the Golgi compartment and that polysialylated proteins are continuously released for at least 24 h after the onset of inflammatory stimulation. The latter was unexpected, because polySia signals detected by immunocytochemistry are rapidly depleted. However, it indicates that the amount of released polySia is much higher than anticipated based on immunostaining. This may be crucial for microglial responses during traumatic brain injury (TBI), as we detected polySia signals in activated microglia around a stab wound in the adult mouse brain. In BV2 microglia, the putative polySia receptor Siglec-E is internalized during lipopolysaccharide (LPS)-induced activation and in response to polySia exposure, indicating interaction. Correspondingly, CRISPR/Cas9-mediated Siglec-E knockout prevents inhibition of pro inflammatory activation by exogenously added polySia and leads to a strong increase of the LPS response. A comparable increase of LPS-induced activation has been observed in microglia with abolished polySia synthesis. Together, these results indicate that the release of the microglia-intrinsic polySia pool, as implicated in TBI, inhibits the inflammatory response by acting as a trans-activating ligand of Siglec-E.

A novel compound DBZ ameliorates neuroinflammation in LPS-stimulated microglia and ischemic stroke rats: Role of Akt(Ser473)/GSK3β(Ser9)-mediated Nrf2 activation

Microglia-mediated neuroinflammation plays a crucial role in the pathophysiological process of multiple neurological disorders such as ischemic stroke, yet lacks effective therapeutic agents. Previously, we discovered one novel synthetic compound, tanshinol borneol ester (DBZ), possesses anti-inflammatory and anti-atherosclerotic activities, whereas little is known about its effects in CNS. Therefore, the present study aims to explore the effects and potential mechanism of DBZ on neuroinflammation and microglial function. Our studies revealed that DBZ significantly inhibited NF-κB activity, suppressed the production of pro-inflammatory mediators meanwhile promoted M2 mediators expression in LPS-stimulated BV2 cells and mouse primary microglia cells. DBZ also exhibited antioxidant activity by enhancing Nrf2 nuclear accumulation and transcriptional activity, increasing HO-1 and NQO1 expression, and inhibiting LPS-induced ROS generation in BV2 cells. Importantly, the anti-neuroinflammatory and antioxidant effects of DBZ above were reversed by Nrf2 knockdown. Additionally, DBZ ameliorated sickness behaviors of neuroinflammatory mice induced by systemic LPS administration, and significantly reduced infract volume, improved sensorimotor and cognitive function in rats subjected to transient middle cerebral artery occlusion (tMCAO); besides, DBZ restored microglia morphological alterations and shifted the M1/M2 polarization in both murine models. Mechanistically, DBZ-induced Nrf2 nuclear accumulation and antioxidant enzymes expression were accompanied by increased level of p-Akt(Ser473) (activation) and p-GSK3β(Ser9) (inactivation), and decreased nuclear level of Fyn both in vitro and in vivo. Pharmacologically inhibiting PI3K or activating GSK3β markedly increased nuclear density of Fyn in microglia cells, which blocked the promoting effect of DBZ on Nrf2 nuclear accumulation and its antioxidant and anti-neuroinflammatory activities. Collectively, these results indicated the effects of DBZ on microglia-mediated neuroinflammation were strongly associated with the nuclear accumulation and stabilization of Nrf2 via the Akt(Ser473)/GSK3β(Ser9)/Fyn pathway. With anti-neuroinflammatory and antioxidant properties, DBZ could be a promising new drug candidate for prevention and/or treatment of cerebral ischemia and other neuroinflammatory disorders.

Phenotypic Differences in Primary Murine Microglia Treated with NOD1, NOD2, and NOD1/2 Agonists

The purpose of the study was studying the influence of different NOD agonists on the morphological phenotype of primary murine microglia and to examine their influence on characteristic cytokines. Primary CD11b-positive cells were isolated from the brain of neonatal mice. The microglial phenotype of the cells was examined by ionized calcium-binding adapter molecule (Iba)1 staining. After14 days in culture, these cells were stimulated by iE-DAP, L18-MDP, or M-TriDAP as NOD1, NOD2, and NOD1/2 agonists, respectively. The cellular morphology was recorded and compared to the phenotype of cells cultured in medium alone or after LPS stimulation. The cells developed a specific phenotype only after treatment with the NOD2 agonist L18-MDP. These cells were characterized by straight extensions carrying tiny spikes and had a high ramification index. This was in sharp contrast to all other treatments, which always resulted in an amoeboid phenotype typically shown by activated microglia in vivo and by cultured microglia in vitro. The staining intensity of IL-6 and TNF-α did not reveal any clear difference independent of the NOD agonist treatment. In contrast, an increased staining intensity was observed for IL-10 after L18-MDP treatment. The NOD2 agonist L18-MDP induced a morphologically distinct phenotype characterized by microspike-decorated dendritiform extensions and a high degree of ramification in primary murine microglia. Increased ramification index and elevated staining intensity of anti-inflammatory IL-10 as hallmarks suggest that a M2-like phenotype of microglia was induced.

Nafamostat mesylate attenuates the pathophysiologic sequelae of neurovascular ischemia

Nafamostat mesylate, an apparent soi-disant panacea of sorts, is widely used to anticoagulate patients undergoing hemodialysis or cardiopulmonary bypass, mitigate the inflammatory response in patients diagnosed with acute pancreatitis, and reverse the coagulopathy of patients experiencing the commonly preterminal disseminated intravascular coagulation in the Far East. The serine protease inhibitor nafamostat mesylate exhibits significant neuroprotective effects in the setting of neurovascular ischemia. Nafamostat mesylate generates neuroprotective effects by attenuating the enzymatic activity of serine proteases, neuroinflammatory signaling cascades, and the endoplasmic reticulum stress responses, downregulating excitotoxic transient receptor membrane channel subfamily 7 cationic currents, modulating the activity of intracellular signal transduction pathways, and supporting neuronal survival (brain-derived neurotrophic factor/TrkB/ERK1/2/CREB, nuclear factor kappa B. The effects collectively reduce neuronal necrosis and apoptosis and prevent ischemia mediated disruption of blood-brain barrier microarchitecture. Investigational clinical applications of these compounds may mitigate ischemic reperfusion injury in patients undergoing cardiac, hepatic, renal, or intestinal transplant, preventing allograft rejection, and treating solid organ malignancies. Neuroprotective effects mediated by nafamostat mesylate support the wise conduct of randomized prospective controlled trials in Western countries to evaluate the clinical utility of this compound.

Achyranthes bidentata polypeptide k suppresses neuroinflammation in BV2 microglia through Nrf2-dependent mechanism

Background

Activated microglia play a critical role in regulating neuroinflammatory responses in central nervous system. Previous studies have shown that Achyranthes bidentata polypeptide k's (ABPPk's) neuroprotective effects are partly due to its anti-inflammatory effect, but the mechanism remains unknown. This study is aimed to investigate the anti-inflammatory effect of ABPPk on lipopolysaccharide (LPS)-activated neuroinflammation in BV2 microglia.

Methods

We pretreated BV2 microglia with different concentrations of ABPPk (0.04-5 µg/mL) for 30 minutes, and then stimulated microglia with LPS for 24 hours. Pro-inflammatory mediators including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), nitric oxide (NO) and prostaglandin E₂ (PGE₂) production were measured by enzyme-linked immunosorbent assay (ELISA) kits. Inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), phosphorylated nuclear factor kappa B (NF-κB), heme oxygenase-1 (HO-1) and nuclear factor erythroid 2-related factor 2 (Nrf2) expression levels were detected by western blot. Glutathione (GSH) level was measured by GSH-Glo™ Glutathione assay. Immunofluorescent staining was used to detect the nuclear translocation of NF-κB and Nrf2. BV2 microglia transfected with Nrf2 siRNA were used to investigate the effect of Nrf2 on the anti-inflammatory activity of ABPPk.

Results

ABPPk (0.2-5 µg/mL) reduced the iNOS mediated NO and COX-2 mediated PGE₂ production significantly in LPS-activated BV2 microglia. ABPPk (1 and 5 µg/mL) also suppressed the production of TNF-α and IL-6 significantly. NF-κB is phosphorylated and translocated into nuclear in LPS-activated BV2 microglia, but ABPPk is shown to inhibit the phosphorylation and translocation of NF-κB in a concentration-dependent way. ABPPk increased the protein expression levels of HO-1 and Nrf2, as well as the GSH content in BV2 microglia. Immunofluorescent staining showed that ABPPk also promoted nuclear translocation of Nrf2. After knocking down Nrf2 in BV2 cells with siRNA interference, ABPPk's inhibitory effect on pro-inflammatory mediators also disappeared.

Conclusions

The present study suggests that ABPPk inhibits neuroinflammation in BV2 microglia through Nrf2-dependent mechanism. This provides some strong evidence for the potential of this neuroprotective natural compound to treat neurodegenerative diseases such as ischemic stroke and Parkinson's disease.

Retinal microglia initiate neuroinflammation in ocular autoimmunity

Autoimmune uveitis is a sight-threatening ocular inflammatory condition in which the retina and uveal tissues become a target of autoreactive immune cells. While microglia have been studied extensively in autoimmune uveitis, their exact function remains uncertain. The objective of the current study was to determine whether resident microglia are necessary and sufficient to initiate and amplify retinal inflammation in autoimmune uveitis. In this study, we clearly demonstrate that microglia are essential for initiating infiltration of immune cells utilizing a murine model of experimental autoimmune uveoretinitis (EAU) and the recently identified microglia-specific marker P2ry12. Initiating disease is the primary function of microglia in EAU, since eliminating microglia during the later stages of EAU had little effect, indicating that the function of circulating leukocytes is to amplify and sustain destructive inflammation once microglia have triggered disease. In the absence of microglia, uveitis does not develop, since leukocytes cannot gain entry through the blood-retinal barrier, illustrating that microglia play a critical role in regulating infiltration of inflammatory cells into the retina.

AMD-Associated HTRA1 Variants Do Not Influence TGF-β Signaling in Microglia

Genetic variants of high-temperature requirement A serine peptidase 1 (HTRA1) and age-related maculopathy susceptibility 2 (ARMS2) are associated with age-related macular degeneration (AMD). One HTRA1 single nucleotide polymorphism (SNP) is situated in the promotor region (rs11200638) resulting in increased expression, while two synonymous SNPs are located in exon 1 (rs1049331:C > T, rs2293870:G > T). HtrA1 is known to inhibit transforming growth factor-β (TGF-β) signaling, a pathway regulating quiescence of microglia, the resident immune cells of the brain and retina. Microglia-mediated immune responses contribute to AMD pathogenesis. It is currently unclear whether AMD-associated HTRA1 variants influence TGF-β signaling and microglia phenotypes. Here, we show that an HtrA1 isoform carrying AMD-associated SNPs in exon 1 exhibits increased proteolytic activity. However, when incubating TGF-β-treated reactive microglia with HtrA1 protein variants, neither the wildtype nor the SNP-associated isoforms changed microglia activation in vitro.

Immunomodulation with minocycline rescues retinal degeneration in juvenile neuronal ceroid lipofuscinosis mice highly susceptible to light damage

Juvenile neuronal ceroid lipofuscinosis (jNCL) is a rare but fatal inherited lysosomal storage disorder mainly affecting children. The disease is caused by mutations in the CLN3 gene that lead to the accumulation of storage material in many tissues, prominent immune responses and neuronal degeneration. One of the first symptoms is vision loss followed by motor dysfunction and mental decline. The established Cln3^Δex7/8 mouse model mimics many pathological features of the human disease except the retinal phenotype, which is very mild and occurs only very late in these mice. Here, we first carefully analyzed the retinal structure and microglia responses in these animals. While prominent autofluorescent spots were present in the fundus, only a moderate reduction of retinal thickness and no prominent microgliosis was seen in young CLN3-deficient mice. We next genetically introduced a light-sensitive RPE65 variant and established a light-damage paradigm that showed a high susceptibility of young Cln3^Δex7/8 mice after exposure to 10,000 lux bright light for 30 min. Under these ‘low light’ conditions, CLN3-deficient mice showed a strong retinal degeneration, microglial activation, deposition of autofluorescent material and transcriptomic changes compared to wild-type animals. Finally, we treated the light-exposed Cln3^Δex7/8 animals with the immunomodulatory compound minocycline, and thereby rescued the retinal phenotype and diminished microgliosis. Our findings indicate that exposure to specific light conditions accelerates CLN3-dependent retinal degeneration, and that immunomodulation by minocycline could be a possible treatment option to delay vision loss in jNCL patients.

This article has an associated First Person interview with the first author of the paper.

Summary: Here, we established a light-damage paradigm to model retinal degeneration in the juvenile neuronal ceroid lipofuscinosis mouse and showed the beneficial effects of minocycline on retinal pathology.

Retinal microglia - A key player in healthy and diseased retina

Microglia, the resident immune cells of the brain and retina, are constantly engaged in the surveillance of their surrounding neural tissue. During embryonic development they infiltrate the retinal tissues and participate in the phagocytosis of redundant neurons. The contribution of microglia in maintaining the purposeful and functional histo-architecture of the adult retina is indispensable. Within the retinal microenvironment, robust microglial activation is elicited by subtle changes caused by extrinsic and intrinsic factors. When there is a disturbance in the cell-cell communication between microglia and other retinal cells, for example in retinal injury, the activated microglia can manifest actions that can be detrimental. This is evidenced by activated microglia secreting inflammatory mediators that can further aggravate the retinal injury. Microglial activation as a harbinger of a variety of retinal diseases is well documented by many studies. In addition, a change in the microglial phenotype which may be associated with aging, may predispose the retina to age-related diseases. In light of the above, the focus of this review is to highlight the role played by microglia in the healthy and diseased retina, based on findings of our own work and from that of others.

Toll-Like Receptor 2 Signaling and Current Approaches for Therapeutic Modulation in Synucleinopathies

The innate immune response in the central nervous system (CNS) is implicated as both beneficial and detrimental to health. Integral to this process are microglia, the resident immune cells of the CNS. Microglia express a wide variety of pattern-recognition receptors, such as Toll-like receptors, that detect changes in the neural environment. The activation of microglia and the subsequent proinflammatory response has become increasingly relevant to synucleinopathies, including Parkinson's disease the second most prevalent neurodegenerative disease. Within these diseases there is evidence of the accumulation of endogenous α-synuclein that stimulates an inflammatory response from microglia via the Toll-like receptors. There have been recent developments in both new and old pharmacological agents designed to target microglia and curtail the inflammatory environment. This review will aim to delineate the process of microglia-mediated inflammation and new therapeutic avenues to manage the response.

Blockade of microglial adenosine A2A receptor impacts inflammatory mechanisms, reduces ARPE-19 cell dysfunction and prevents photoreceptor loss in vitro

Age-related macular degeneration (AMD) is characterized by pathological changes in the retinal pigment epithelium (RPE) and loss of photoreceptors. Growing evidence has demonstrated that reactive microglial cells trigger RPE dysfunction and loss of photoreceptors, and inflammasome pathways and complement activation contribute to AMD pathogenesis. We and others have previously shown that adenosine A_2A receptor (A_2AR) blockade prevents microglia-mediated neuroinflammatory processes and mediates protection to the retina. However, it is still unknown whether blocking A_2AR in microglia protects against the pathological features of AMD. Herein, we show that an A_2AR antagonist, SCH58261, prevents the upregulation of the expression of pro-inflammatory mediators and the alterations in the complement system triggered by an inflammatory challenge in human microglial cells. Furthermore, blockade of A_2AR in microglia decreases the inflammatory response, as well as complement and inflammasome activation, in ARPE-19 cells exposed to conditioned medium of activated microglia. Finally, we also show that blocking A_2AR in human microglia increases the clearance of apoptotic photoreceptors. This study opens the possibility of using selective A_2AR antagonists in therapy for AMD, by modulating the interplay between microglia, RPE and photoreceptors.

Crocin, a plant-derived carotenoid, modulates microglial reactivity

Microglia activation plays an important role in immune responses in the CNS including the retina. Crocin, a plant-derived carotenoid, has been reported to possess anti-inflammatory, anti-apoptotic and anti-oxidative capacity in models of retinal damage and degeneration. If these neuroprotective effects could be mediated by direct modulation of microglial cells is unclear. Here, we examined the direct effects of crocin on key functions and pro-inflammatory gene expression in lipopolysaccharide (LPS)-activated BV-2 microglia. We found that crocin stimulation strongly promoted filopodia formation and markedly increased microglial phagocytosis, two important parameters relevant for physiological microglia functions. Moreover, crocin significantly reduced gene expression of the pro-inflammatory markers IL6, CCL2, and iNOS in LPS-challenged BV-2 cells and potently blocked NO production in these microglia. The observed immunomodulatory effects of crocin were not mediated by general inhibition of NFkB nuclear translocation. Our findings indicate that many of the anti-inflammatory effects of crocin demonstrated in animal models of neuronal degeneration could be mediated by its direct effects on microglia homeostasis.

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Crocin promotes microglial filopodia formation.

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Crocin induces the phagocytic capacity of microglia.

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Crocin dampens LPS-induced pro-inflammatory gene expression and lowers nitric oxide production in microglia.

Comprehensive analysis of mouse retinal mononuclear phagocytes

The innate immune system is activated in a number of degenerative and inflammatory retinal disorders such as age-related macular degeneration (AMD). Retinal microglia, choroidal macrophages, and recruited monocytes, collectively termed 'retinal mononuclear phagocytes', are critical determinants of ocular disease outcome. Many publications have described the presence of these cells in mouse models for retinal disease; however, only limited aspects of their behavior have been uncovered, and these have only been uncovered using a single detection method. The workflow presented here describes a comprehensive analysis strategy that allows characterization of retinal mononuclear phagocytes in vivo and in situ. We present standardized working steps for scanning laser ophthalmoscopy of microglia from MacGreen reporter mice (mice expressing the macrophage colony-stimulating factor receptor GFP transgene throughout the mononuclear phagocyte system), quantitative analysis of Iba1-stained retinal sections and flat mounts, CD11b-based retinal flow cytometry, and qRT-PCR analysis of key microglia markers. The protocol can be completed within 3 d, and we present data from retinas treated with laser-induced choroidal neovascularization (CNV), bright white-light exposure, and Fam161a-associated inherited retinal degeneration. The assays can be applied to any of the existing mouse models for retinal disorders and may be valuable for documenting immune responses in studies for immunomodulatory therapies.

Intramembranous processing by γ-secretase regulates reverse signaling of ephrin-B2 in migration of microglia

The Eph-ephrin system plays pivotal roles in cell adhesion and migration. The receptor-like functions of the ephrin ligands allow the regulation of intracellular processes via reverse signaling. γ-Secretase mediated processing of ephrin-B has previously been linked to activation of Src, a kinase crucial for focal adhesion and podosome phosphorylation. Here, we analyzed the role of γ-secretase in the stimulation of reverse ephrin-B2 signaling in the migration of mouse embryonic stem cell derived microglia. The proteolytic generation of the ephrin-B2 intracellular domain (ICD) by γ-secretase stimulates Src and focal adhesion kinase (FAK). Inhibition of γ-secretase decreased the phosphorylation of Src and FAK, and reduced cell motility. These effects were associated with enlargement of the podosomal surface. Interestingly, expression of ephrin-B2 ICD could rescue these effects, indicating that this proteolytic fragment mediates the activation of Src and FAK, and thereby regulates podosomal dynamics in microglial cells. Together, these results identify γ-secretase as well as ephrin-B2 as regulators of microglial migration.

Shizukaol B, an active sesquiterpene from Chloranthus henryi, attenuates LPS-induced inflammatory responses in BV2 microglial cells

The objective of the current study was to evaluate the anti-inflammatory effects of shizukaol B, a lindenane-type dimeric sesquiterpene isolated from the whole plant of Chloranthus henryi, on lipopolysaccharide (LPS)-induced activation of BV2 microglial cells in vitro. Our data showed that shizukaol B concentration-dependently suppressed expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), production of nitric oxide (NO), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) in LPS-stimulated BV2 microglia. Meanwhile, shizukaol B concentration- and time-dependently inhibited LPS-mediated c-Jun N-terminal kinase 1/2 (JNK) activation, but had little effect on extracellular signal-regulated kinase 1/2 or p38 phosphorylation. Furthermore, shizukaol B significantly blocked LPS-induced activator protein-1 (AP-1) activation, evidenced by reduced phosphorylation and nuclear translocation of c-Jun and DNA binding activity of AP-1. Taken together, our findings suggest that shizukaol B exerts anti-inflammatory effects in LPS-activated microglia partly by modulating JNK-AP-1 signaling pathway.

PERK and XBP1 differentially regulate CXCL10 and CCL2 production

Inflammation plays a key role in the pathogenesis of many retinal degenerative diseases related with photoreceptor dysfunction/degeneration. However the involvement of photoreceptor cells in inflammatory reactions is largely unknown as they are not considered as inflammatory cells. In this study, we assessed whether photoreceptor cells can produce CCL2 and CXCL10, two important players in inflammation during endoplasmic reticulum (ER) stress. After photoreceptor 661 W cells were treated with ER stress inducer thapsigargin (TG), induction of ER stress increased CXCL10 and CCL2 expression at both mRNA and protein levels, which was significantly blocked by an ER stress blocker 4-phenylbutyrate. ER stress contains three pathways: PERK, ATF6 and IRE1α. Knockdown of PERK attenuated TG-induced CXCL10 and CCL2 mRNA expression, associated with significant decreases in phosphorylation of NF-κB RelA and STAT3. In contrast to PERK, knockdown of XBP1, which is activated by IRE1α-mediated splicing, robustly enhanced TG-induced CXCL10 and CCL2 expression and phosphorylation of NF-κB RelA and STAT3. Blockade of NF-κB or STAT3 markedly diminished TG-induced CXCL10 and CCL2 expression. The specific roles of PERK and XBP1 in CXCL10 and CCL2 expression were further investigated by treating photoreceptor cells with advanced glycation end products (AGE) and high glucose (HG), two of the major contributors to diabetic complications. Similarly, AGE and HG induced CXCL10 and CCL2 expression in which PERK was a positive regulator while XBP1 was a negative regulator. These studies suggest that photoreceptors may be involved in retinal inflammation by expressing chemokines CXCL10 and CCL2. PERK and IRE1α/XBP1 in the unfolded protein response differentially regulate the expression of CXCL10 and CCL2 likely through modulation of ER stress-induced NF-κB RelA and STAT3 activation.

Upregulation of AMWAP: a novel mechanism for HDAC inhibitors to protect against cisplatin nephrotoxicity

Histone deacetylases have been reported to protect against renal tubular damage in several animal models of acute renal injury, including cisplatin nephrotoxicity. However, the mechanism involved is not well defined. In this study, Ranganathan et al. identify activated microglia/macrophage WAP domain protein as the novel mediator of histone deacetylase inhibitor-mediated renal protection in a murine model of cisplatin nephrotoxicity. Activated microglia/macrophage WAP-mediated renal protection is associated with suppression of inflammation and renal epithelial cell apoptosis.

Nafamostat mesilate improves function recovery after stroke by inhibiting neuroinflammation in rats

Inflammation plays an important role in stroke pathology, making it a promising target for stroke intervention. Nafamostat mesilate (NM), a wide-spectrum serine protease inhibitor, is commonly used for treating inflammatory diseases, such as pancreatitis. However, its effect on neuroinflammation after stroke was unknown. Hence, the effects of NM on the inflammatory response post stroke were characterized. After transient middle cerebral artery occlusion (tMCAO) in rats, NM reduced the infarct size, improved behavioral functions, decreased the expression of proinflammatory mediators (TNF-α, IL-1β, iNOS and COX-2) in a time-dependent manner and promoted the expression of different anti-inflammatory factors (CD206, TGF-β, IL-10 and IL-4) at different time points. Furthermore, NM could inhibit the expression of proinflammatory mediators and promote anti-inflammatory mediators expression in rat primary microglia following exposure to thrombin combined with oxygen-glucose deprivation (OGD). The immune-modulatory effect of NM might be partly due to its inhibition of the NF-κB signaling pathway and inflammasome activation after tMCAO. In addition, NM significantly inhibited the infiltration of macrophage, neutrophil and T lymphocytes, which was partly mediated by the inhibition of monocyte chemotactic protein-1 (MCP-1), intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). Taken together, our results indicated that NM can provide long-term protection of the brain against tMCAO by modulating a broad components of the inflammatory response.

Friend or Foe? Resident Microglia vs Bone Marrow-Derived Microglia and Their Roles in the Retinal Degeneration

Microglia are immune cells in the central nervous system (CNS) that originate from the yolk sac in an embryo. The renewal of the microglia pool in the adult eye consists of two components. In addition to the self-proliferation of resident cells, microglia in the CNS also derive from the bone marrow (BM). BM-derived cells pass through the blood-brain barrier (BBB) or blood-retina barrier (BRB) and differentiate into microglia under specific conditions which involves a complex mechanism. Recent studies have widely investigated the role of resident microglia and BM-derived microglia in the retinal degenerative disease. Both two cell types play dual roles and share many similar functions. However, resident microglia tend to polarize to the M1 phenotype which is pro-inflammatory and neurotoxic, whereas BM-derived microglia mainly polarize to the neuroprotective M2 phenotype in retinal degeneration. The molecular mechanism that underlines the invasion of peripheral cells has led to extensive discussions. In addition to the BBB and BRB disruption, many signaling pathways are involved in this process. Based on these studies, we discuss the roles of these two types of microglia in retinal degeneration disease and the potential clinical application of BM-derived microglia, which may benefit future therapies.

Effects of maternal exposure to di-n-butyl phthalate during pregnancy and breastfeeding on ovarian development and function of F1 female rats

This study aimed to investigate the effects of maternal exposure to di-n-butyl phthalate (DBP) during pregnancy and breastfeeding on F1 ovarian development and function. A rat model of maternal exposure to DBP during pregnancy and breastfeeding was established by gavage feeding female Sprague Dawley rats with 0, 10, 100, or 600mg/kg/day DBP from gestational day (GD) 12 to postnatal day (PND) 21. F1 offspring were weaned on PND21 and were not exposed to DBP afterward. The age of vaginal opening and estrus onset, estrous cyclicity, c-Kit-ligand expression on ovarian granulosa cells, and the weight of ovaries and uterus of F1 female offspring were not affected, whereas serum levels of estradiol and progesterone were increased significantly by maternal exposure to 10mg/kg/day DBP from GD12 to PND21. Although F1 ovarian function may not be adversely affected by maternal exposure to DBP, the increased reproductive hormone levels may interfere in F1 rat fertility.

TLR4 Signaling in MPP⁺-Induced Activation of BV-2 Cells

Aims. This work was conducted to establish an in vitro Parkinson's disease (PD) model by exposing BV-2 cells to 1-methyl-4-phenylpyridinium (MPP⁺) and exploring the roles of TLR2/TLR4/TLR9 in inflammatory responses to MPP⁺. Methods/Results. MTT assay showed that cell viability of BV-2 cells was 84.78 ± 0.86% and 81.18 ± 0.99% of the control after incubation with 0.1 mM MPP⁺ for 12 hours and 24 hours, respectively. Viability was not significantly different from the control group. With immunofluorescence technique, we found that MPP⁺ incubation at 0.1 mM for 12 hours was the best condition to activate BV-2 cells. In this condition, the levels of TNF-α, IL-1β, and iNOS protein were statistically increased compared to the control according to ELISA tests. Real time RT-PCR and western blot measurements showed that TLR4 was statistically increased after 0.1 mM MPP⁺ incubation for 12 hours. Furthermore, after siRNA interference of TLR4 mRNA, NF-κB activation and the levels of TNF-α, IL-1β, and iNOS were all statistically decreased in this cell model. Conclusion. MPP⁺ incubation at the concentration of 0.1 mM for 12 hours is the best condition to activate BV-2 cells for mimicking PD inflammation in BV-2 cells. TLR4 signalling plays a critical role in the activation of BV-2 cells and the induction of inflammation in this cell model.

Minocycline counter-regulates pro-inflammatory microglia responses in the retina and protects from degeneration

Background

Microglia reactivity is a hallmark of retinal degenerations and overwhelming microglial responses contribute to photoreceptor death. Minocycline, a semi-synthetic tetracycline analog, has potent anti-inflammatory and neuroprotective effects. Here, we investigated how minocycline affects microglia in vitro and studied its immuno-modulatory properties in a mouse model of acute retinal degeneration using bright white light exposure.

Methods

LPS-treated BV-2 microglia were stimulated with 50 μg/ml minocycline for 6 or 24 h, respectively. Pro-inflammatory gene transcription was determined by real-time RT-PCR and nitric oxide (NO) secretion was assessed using the Griess reagent. Caspase 3/7 levels were determined in 661W photoreceptors cultured with microglia-conditioned medium in the absence or presence of minocycline supplementation. BALB/cJ mice received daily intraperitoneal injections of 45 mg/kg minocycline, starting 1 day before exposure to 15.000 lux white light for 1 hour. The effect of minocycline treatment on microglial reactivity was analyzed by immunohistochemical stainings of retinal sections and flat-mounts, and messenger RNA (mRNA) expression of microglia markers was determined using real-time RT-PCR and RNA-sequencing. Optical coherence tomography (OCT) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) stainings were used to measure the extent of retinal degeneration and photoreceptor apoptosis.

Results

Stimulation of LPS-activated BV-2 microglia with minocycline significantly diminished the transcription of the pro-inflammatory markers CCL2, IL6, and inducible nitric oxide synthase (iNOS). Minocycline also reduced the production of NO and dampened microglial neurotoxicity on 661W photoreceptors. Furthermore, minocycline had direct protective effects on 661W photoreceptors by decreasing caspase 3/7 activity. In mice challenged with white light, injections of minocycline strongly decreased the number of amoeboid alerted microglia in the outer retina and down-regulated the expression of the microglial activation marker translocator protein (18 kDa) (TSPO), CD68, and activated microglia/macrophage whey acidic protein (AMWAP) already 1 day after light exposure. Furthermore, RNA-seq analyses revealed the potential of minocycline to globally counter-regulate pro-inflammatory gene transcription in the light-damaged retina. The severe thinning of the outer retina and the strong induction of photoreceptor apoptosis induced by light challenge were nearly completely prevented by minocycline treatment as indicated by a preserved retinal structure and a low number of apoptotic cells.

Conclusions

Minocycline potently counter-regulates microgliosis and light-induced retinal damage, indicating a promising concept for the treatment of retinal pathologies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0431-4) contains supplementary material, which is available to authorized users.

Targeting translocator protein (18 kDa) (TSPO) dampens pro-inflammatory microglia reactivity in the retina and protects from degeneration

BACKGROUND

Reactive microglia are commonly seen in retinal degenerative diseases, and neurotoxic microglia responses can contribute to photoreceptor cell death. We and others have previously shown that translocator protein (18 kDa) (TSPO) is highly induced in retinal degenerations and that the selective TSPO ligand XBD173 (AC-5216, emapunil) exerts strong anti-inflammatory effects on microglia in vitro and ex vivo. Here, we investigated whether targeting TSPO with XBD173 has immuno-modulatory and neuroprotective functions in two mouse models of acute retinal degeneration using bright white light exposure.

METHODS

BALB/cJ and Cx3cr1(GFP/+) mice received intraperitoneal injections of 10 mg/kg XBD173 or vehicle for five consecutive days, starting 1 day prior to exposure to either 15,000 lux white light for 1 h or 50,000 lux focal light for 10 min, respectively. The effects of XBD173 treatment on microglia and Müller cell reactivity were analyzed by immuno-stainings of retinal sections and flat mounts, fluorescence-activated cell sorting (FACS) analysis, and mRNA expression of microglia markers using quantitative real-time PCR (qRT-PCR). Optical coherence tomography (OCT), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) stainings, and morphometric analyses were used to quantify the extent of retinal degeneration and photoreceptor apoptosis.

RESULTS

Four days after the mice were challenged with bright white light, a large number of amoeboid-shaped alerted microglia appeared in the degenerating outer retina, which was nearly completely prevented by treatment with XBD173. This treatment also down-regulated the expression of TSPO protein in microglia but did not change the TSPO levels in the retinal pigment epithelium (RPE). RT-PCR analysis showed that the microglia/macrophage markers Cd68 and activated microglia/macrophage whey acidic protein (Amwap) as well as the pro-inflammatory genes Ccl2 and Il6 were reduced after XBD173 treatment. Light-induced degeneration of the outer retina was nearly fully blocked by XBD173 treatment. We further confirmed these findings in an independent mouse model of focal light damage. Retinas of animals receiving XBD173 therapy displayed significantly more ramified non-reactive microglia and more viable arrestin-positive cone photoreceptors than vehicle controls.

CONCLUSIONS

Targeting TSPO with XBD173 effectively counter-regulates microgliosis and ameliorates light-induced retinal damage, highlighting a new pharmacological concept for the treatment of retinal degenerations.

The microglia in healthy and diseased retina

The microglia are the immune cells of the central nervous system and, also the retina. They fulfil several tasks of surveillance in the healthy retina. In case of an injury or disease, microglia become activated and tries to repair the damage. However, in a lot of cases it does not work, and microglia deteriorate the situation by releasing toxic and pro-inflammatory compounds. Moreover, they further promote degenerative processes by attacking and phagocytosing damaged neurones and photoreceptors that otherwise would possibly have the chance to survive. Such deleterious action of the microglia has been observed in degeneration of retinal ganglion cells and photoreceptors, and it takes place in hereditary diseases, infections as well as in case of traumatic or light injuries. Therefore, a number of attempts has been undertaken so far to inhibit the microglia, with varying success. The task remains to study behaviour of the microglia and their interaction with other retinal cell populations in more detail with respect to released factors and expressed receptors including the time points of the corresponding events. The goal has to be to find a better balance between helpful and detrimental actions of the microglia.