Promote Microglia Activation Research Articles

SIRT1 modulates microglia phenotypes via inhibiting drp1 phosphorylation reduces neuroinflammation in heatstroke

BackgroundBrain injury often results in high mortality rates and significant sequelae following severe heatstroke (HS). Neuroinflammation aggravates HS-induced brain injury, yet the involvement of microglia in heat-induced neuroinflammation deserves further investigation. MethodsOur study investigated activation status, phenotype markers, production of pro-inflammatory cytokine and reactive oxygen species (ROS) of microglia both in vitro and in vivo under HS. Utilizing high-throughput sequencing, we identified SIRT1 as a potential modulator of microglia phenotype, and observed that SIRT1 alleviated severe heatstroke-induced brain injury following intraperitoneal administration of the SIRT1 agonist SRT-1720 and the inhibitor selisistat. Additionally, the effects of SRT-1720 and selisistat on mitochondrial dynamics and microglial phenotype transition were examined in BV2 cells in vitro. ResultsHeatstroke promotes microglia activation, as evidenced by the increased production of pro-inflammatory cytokine and reactive oxygen species. High-throughput sequencing revealed elevated expression of SIRT1 in BV2 cells under HS. Upon inhibition of SIRT1 expression, there was a corresponding increase in pro-inflammatory cytokine, iNOS, and ROS expression in BV2 cells. In vivo experiments with the SIRT1 agonist SRT-1720 showed a mitigation of neuron injury under HS, as assessed by Nissl and HE staining. Activation of SIRT1 was associated with a reduction in mitochondrial injury and a decrease in the phosphorylation of mitochondrial fission protein Drp1ser616. Furthermore, the heat-induced activation of microglia was reversed by the Drp1 inhibitor, Mdivi. ConclusionsOur findings provided evidence that SIRT1 played a crucial role in inhibiting heat stress-induced microglial activation. By suppressing the phosphorylation of mitochondrial fission protein Drp1, SIRT1 contributed to the reduction of neuroinflammation and severity of heatstroke-induced brain injury.

SMAC mimetic drives microglia phenotype and glioblastoma immune microenvironment

Tumor-associated macrophages/microglia (TAMs) are highly plastic and heterogeneous immune cells that can be immune-supportive or tumor-supportive depending of the microenvironment. TAMs are the most abundant immune cells in glioblastoma (GB), and play a key role in immunosuppression. Therefore, TAMs reprogramming toward immune-supportive cells is a promising strategy to overcome immunosuppression. By leveraging scRNAseq human GB databases, we identified that Inhibitor of Apoptosis Proteins (IAP) were expressed by TAMs. To investigate their role in TAMs-related immunosuppression, we antagonized IAP using the central nervous system permeant SMAC mimetic GDC-0152 (SMg). On explants and cultured immune cells isolated from human GB samples, SMg modified TAMs activity. We showed that SMg treatment promoted microglia pro-apoptotic and anti-tumoral function via caspase-3 pro-inflammatory cleavage and the inhibition of tumoroids growth. Then we designed a relevant immunogenic mouse GB model to decipher the spatio-temporal densities, distribution, phenotypes and function of TAMs with or without SMg treatment. We used 3D imaging techniques, a transgenic mouse with fluorescent TAM subsets and mass cytometry. We confirmed that SMg promoted microglia activation, antigen-presenting function and tumor infiltration. In addition, we observed a remodeling of blood vessels, a decrease in anti-inflammatory macrophages and an increased level of monocytes and their mo-DC progeny. This remodeling of the TAM landscape is associated with an increase in CD8 T cell density and activation. Altogether, these results demonstrated that SMg drives the immunosuppressive basal microglia toward an active phenotype with pro-apoptotic and anti-tumoral function and modifies the GB immune landscape. This identifies IAP as targets of choice for a potential mechanism-based therapeutic strategy and SMg as a promising molecule for this application.

GPR34 senses demyelination to promote neuroinflammation and pathologies.

Sterile neuroinflammation is a major driver of multiple neurological diseases. Myelin debris can act as an inflammatory stimulus to promote inflammation and pathologies, but the mechanism is poorly understood. Here, we showed that lysophosphatidylserine (LysoPS)-GPR34 axis played a critical role in microglia-mediated myelin debris sensing and the subsequent neuroinflammation. Myelin debris-induced microglia activation and proinflammatory cytokine expression relied on its lipid component LysoPS. Both myelin debris and LysoPS promoted microglia activation and the production of proinflammatory cytokines via GPR34 and its downstream PI3K-AKT and ERK signaling. In vivo, reducing the content of LysoPS in myelin or inhibition of GPR34 with genetic or pharmacological approaches reduced neuroinflammation and pathologies in the mouse models of multiple sclerosis and stroke. Thus, our results identify GPR34 as a key receptor to sense demyelination and CNS damage and promote neuroinflammation, and suggest it as a potential therapeutic target for demyelination-associated diseases.

Single-nucleus transcriptome unveils the role of ferroptosis in ischemic stroke

Multiple cell death pathways are involved in neuronal death in ischemic stroke (IS). However, the role of different cell death pathways in different cell types has not been elucidated. By analyzing three single-nucleus RNA sequencing (snRNA-seq) data of IS, we first found that a variety of programmed cell death (PCD) -related genes were significantly changed in different cell types. Based on machine learning and virtual gene knockout, we found that ferroptosis related genes, ferritin heavy chain 1 (Fth1) and ferritin light chain (Ftl1), play a key role in IS. Ftl1 and Fth1 can promote microglia activation, as well as the production of inflammatory factors and chemokines. Cell communication analysis showed that activated microglia could enhance chemotactic peripheral leukocyte infiltration, such as macrophages and neutrophils, through Spp1-Cd44 and App-Cd74 signaling, thereby aggravating brain tissue damage. Furthermore, real‐time quantitative polymerase chain reaction (RT‐qPCR) showed that P2ry12 and Mef2c were significantly decreased in oxygen-glucose deprivation (OGD) group, while Ftl1, Fth1, Apoe, Ctsb, Cd44 and Cd74 were significantly increased in OGD group. Collectively, our findings suggested targeted therapy against microglia Ftl1 and Fth1 might improve the state of microglia, reduce the infiltration of peripheral immune cells and tissue inflammation, and then improve the ischemic brain injury in mouse.

LRRK2 regulates ferroptosis through the system Xc-GSH-GPX4 pathway in the neuroinflammatory mechanism of Parkinson's disease.

Parkinson's disease (PD) is the most prevalent neurodegenerative disorder. Neuroinflammation mediated by activated microglia and apoptosis of dopaminergic (DA) neurons in the midbrain are its primary pathological manifestations. Leucine-rich repeat protein kinase 2 (LRRK2) kinase has been observed to increase expression during neuroinflammation,however, the effect of LRRK2 on microglia activation remains poorly understood. In this study, we have established lipopolysaccharide (LPS) treated BV2 cells and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) models for both in vivo and in vitro investigation. Our data in vivo reveal that LRRK2 can promote microglia activation by regulating ferroptosis and activatingnuclear factor-κB. Inhibition of LRRK2 expression effectively suppressed the LPS-induced pro-inflammatory cytokines and facilitated the secretion of neuroprotective factors. Importantly, by co-overexpressing LRRK2 and glutathione peroxidase 4 (GPX4), we identified the system Xc-GSH-GPX4 pathway as a crucial component in LRRK2-mediated microglial ferroptosis and inflammatory responses. Using a microglial culture supernatant (MCS) transfer model, we found that inhibiting LRRK2 or downregulating ferroptosis in BV2 cells prevented SH-SY5Y cell apoptosis. Additionally, we observed abundant expression of LRRK2 and P-P65 in the midbrain, which was elevated in the MPTP-induced PD model, along with microglia activation. LRRK2 and P-P65 expression inhibition with PF-06447475 attenuated microglia activation in the nigrostriatal dense part of MPTP-treated mice. Based on our findings, it is evident that LRRK2 plays a critical role in promoting the neuroinflammatory response during the pathogenesis of PD by regulating the system Xc-GSH-GPX4 pathway. Taken together, our data highlights the potential research and therapeutic value of targeting LRRK2 to regulate neuroinflammatory response in PD through ferroptosis.

FcγRIIb Exacerbates LPS-Induced Neuroinflammation by Binding with the Bridging Protein DAP12 and Promoting the Activation of PI3K/AKT Signaling Pathway in Microglia.

This paper focuses on the expression and role of FcγRIIb in neuroinflammation, exploring the molecular mechanisms by which FcγRIIb interacts with the bridging protein DAP12 to regulate the PI3K-AKT signaling pathway that promote neuroinflammation and aggravate neuronal injury. LPS-induced neuroinflammation models in vivo and in vitro were constructed to explore the role and mechanism of FcγRIIb in CNS inflammation. Subsequently, FcγRIIb was knocked down or overexpressed to observe the activation of BV2 cell and the effect on PI3K-AKT pathway. Then the PI3K-AKT pathway was blocked to observe its effect on cell activation and FcγRIIb expression. We analyzed the interaction between FcγRIIb and DAP12 by Immunoprecipitation technique. Then FcγRIIb was overexpressed while knocking down DAP12 to observe its effect on PI3K-AKT pathway. Finally, BV2 cell culture supernatant was co-cultured with neuronal cell HT22 to observe its effect on neuronal apoptosis and cell activity. In vivo and in vitro, we found that FcγRIIb expression was significantly increased and activated the PI3K-AKT pathway. Contrary to the results of overexpression of FcγRIIb, knockdown of FcγRIIb resulted in a significant low level of relevant inflammatory factors and suppressed the PI3K-AKT pathway. Furthermore, LPS stimulation induced an interaction between FcγRIIb and DAP12. Knockdown of DAP12 suppressed inflammation and activation of the PI3K-AKT pathway in BV2 cells, and meantime overexpression of FcγRIIb suppressed the level of FcγRIIb-induced AKT phosphorylation. Additionally, knockdown of FcγRIIb inhibited microglia activation, which induced neuronal apoptosis. Altogether, our experiments indicate that FcγRIIb interacts with DAP12 to promote microglia activation by activating the PI3K-AKT pathway while leading to neuronal apoptosis and exacerbating brain tissue injury, which may provide a new target for the treatment of inflammatory diseases in the central nervous system.

Stretch-injury promotes microglia activation with enhanced phagocytic and synaptic stripping activities

Microglial cells, as the primary defense line in the central nervous system, play a crucial role in responding to various mechanical signals that can trigger their activation. Despite extensive research on the impact of chemical signaling on brain cells, the understanding of mechanical signaling in microglia remains limited. To bridge this gap, we subjected microglial cells to a singular mechanical stretch and compared their responses with those induced by lipopolysaccharide treatment, a well-established chemical activator. Here we show that stretching microglial cells leads to their activation, highlighting their significant mechanosensitivity. Stretched microglial cells exhibited distinct features, including elevated levels of Iba1 protein, a denser actin cytoskeleton, and increased persistence in migration. Unlike LPS-treated microglial cells, the secretory profile of chemokines and cytokines remained largely unchanged in response to stretching, except for TNF-α. Intriguingly, a single stretch injury resulted in more compacted chromatin and DNA damage, suggesting potential long-term genomic instabilities in stretched microglia. Using compartmentalized microfluidic chambers with neuronal networks, we observed that stretched microglial cells exhibited enhanced phagocytic and synaptic stripping activities. These findings collectively suggest that stretching events can unlock the immune potential of microglial cells, contributing to the maintenance of brain tissue homeostasis following mechanical injury.

Single-Cell RNA Sequencing Transcriptomics Revealed HCMV IE2-Related Microglia Responses in Alzheimer's-Like Disease in Transgenic Mice.

Although multiple factors are known to concur with Alzheimer's disease (AD), the relationship between human cytomegalovirus (HCMV) and AD-like disease is unclear. Here, we propose a hypothesis that HCMV immediate-early 2 (IE2) protein promotes microglia activation and thus leads to AD-like disease. We successfully constructed IE2 transgenic mice expressing IE2 in the hippocampus. Single-cell sequencing analysis revealed that IE2 promoted the activation of microglia and upregulated the expression of disease-associated microglia genes. Differentially expressed gene analysis and pathway enrichment revealed that IE2 upregulated immune and nervous system disease-related genes. Immunohistochemical analysis showed that the expressions of both amyloid precursor protein (APP) and p-Tau were significantly upregulated in the brains of IE2 mice and were markers of AD. Taken together, these findings provide useful insights into AD-like disease activated by HCMV IE2.

GKLF, a transcriptional activator of Txnip, drives microglia activation in kainic acid-induced murine models of epileptic seizures.

Neuroinflammation is a major component of epilepsy. Gut-enriched Kruppel-like factor (GKLF), a transcription factor of Kruppel-like factor family, has been reported to promote microglia activation and mediate neuroinflammation. However, the role of GKLF in epilepsy remains poorly characterized. This study focused on the function of GKLF in neuron loss and neuroinflammation in epilepsy and the molecular mechanism underlying microglia activation induced by GKLF upon lipopolysaccharides (LPS) treatment. An experimental epileptic model was induced by an intraperitoneal injection of 25mg/kg kainic acid (KA). Lentivirus vectors (Lv) carrying Gklf CDS or short hairpin RNA targeting Gklf (shGKLF) was injected into the hippocampus, resulting in Gklf overexpression or knockdown in the hippocampus. BV-2 cells were co-infected with Lv-shGKLF or/and Lv carrying thioredoxin interacting protein (Txnip) CDS for 48h and treated with 1μg/mL LPS for 24h. Results showed that GKLF enhanced KA-induced neuronal loss, pro-inflammatory cytokine secretion, activation of NOD-like receptor protein-3 (NLRP3) inflammasomes and microglia, and TXNIP expression in the hippocampus. GKLF inhibition showed negative effects on LPS-induced microglia activation, as evidenced by reduced pro-inflammatory cytokine secretion and activation of NLRP3 inflammasomes. GKLF bound to Txnip promoter and increased TXNIP expression in LPS-activated microglia. Interestingly, Txnip overexpression reversed the inhibitory effect of Gklf knockdown on microglia activation. These findings indicated that GKLF was involved in microglia activation via TXNIP. This study demonstrates the underlying mechanism of GKLF in the pathogenesis of epilepsy and uncovers that GKLF inhibition may be a therapeutic strategy for epilepsy treatment.

MiR-19a-3p and miR-19b-3p promote microglia activation associated with neuroinflammation following spinal cord injury

Abstract Spinal cord injury (SCI)-induced neuropathic pain represents a significant clinical challenge that affects 10 to 30% of injured persons. Following SCI, microglia activation promotes neuroinflammation through the production of pro-inflammatory cytokines which has been suggested to play a role in neuropathic pain. MicroRNAs (miRs) can be molecular mediators of neuroinflammation. Our group has shown elevated levels of circulating miR-19a and miR-19b in persons living with chronic pain following SCI. We wanted to determine whether miR-19a and miR-19b are involved in neuroinflammation mediated by activated microglia after SCI. Microglia were incubated with inflammatory stimuli in the presence of miR-19a or miR-19b mimics and analyzed for activation. Microglia activation was enhanced in the presence of miR-19a or miR-19b mimics with increased expression of pro-inflammatory cytokines and decreased expression of suppressor of cytokine signaling, SOCS1 and SOCS3. Further, our results show enhanced signaling via NF-kB and Jak pathways. Overall, our results showed that treatment of microglia with miR-19a or miR-19b inhibited SOCS1 and SOCS3 expression and promoted expression of pro-inflammatory cytokines resulting in enhanced microglia activation. These results suggest that increased expression of miR-19a and miR-19b after SCI may be promoting neuroinflammation through activation of the microglia which contributes to neuropathic pain. These results may be useful in developing therapies targeting miRNAs to control neuroinflammation and neuropathic pain in persons living with SCI. This study was supported by the Department of Defense (W81XWH-10-1-1043), National Institutes of Health (R01AR064793) and The National Institute on Disability, Independent Living, and Rehabilitation Research (NIDILRR, 90SI5015-01-00)

Microglia and status epilepticus in the immature brain.

Microglia are the resident immune cells of the Central Nervous System (CNS), which are activated due to brain damage, as part of the neuroinflammatory response. Microglia undergo morphological and biochemical modifications during activation, adopting a pro-inflammatory or an antiinflammatory state. In the developing brain, status epilepticus (SE) promotes microglia activation that is associated with neuronal injury in some areas of the brain, such as the hippocampus, thalamus, and amygdala. However, the timing of this activation, the anatomical pattern, and the morphological and biochemical characteristics of microglia in the immature brain are age-dependent and have not been fully characterized. Therefore, this review focuses on the response of microglia to SE and its relationship to neurodegeneration.

Propofol alleviates postoperative cognitive dysfunction by inhibiting inflammation via up-regulating miR-223-3p in aged rats.

Postoperative cognitive dysfunction (POCD) affects 15-25% of surgical patients and causes significant morbidity and mortality. This study aims to investigate the mechanism of propofol reducing POCD in aged rats. Rats in Operate group and Propofol group were anesthetized with isoflurane and propofol, respectively, and then underwent cardiac surgery. Rats in Antagomir group were anesthetized with propofol and underwent cardiac surgery with preoperative injection of miR-223-3p antagomir. Barnes maze and Morris water maze (MWM) were used to test spatial learning and memory of rats. Immunofluorescence was used to detect the level of microglial cell marker IBA1. In addition, qRT-PCR was performed to measure the expression of miR-223-3p and inflammatory factors TNF-α, IL-1β and IL-6. Western blotting was conducted to detect the protein expression of Foxo1, TNF-α, IL-1β and IL-6. Isoflurane-anesthetized rats undergoing cardiac surgery showed significantly reduced spatial learning and memory, promoted microglia activation, decreased miR-223-3p expression and increased inflammatory response in the hippocampus, while isoflurane-anesthetized rats without surgery showed insignificant changes in these indices. Compared to isoflurane anesthesia, propofol anesthesia exhibited less effect on spatial learning and memory of rats with cardiac surgery and contributed to a relative reduction in activated microglia in the hippocampus, a notable increase in miR-223-3p expression, and a decrease in inflammation. The results were reversed after miR-223-3p antagomir was injected into propofol-anesthetized surgical rats. miR-223-3p negatively regulated Foxo1 to suppress the expression of inflammatory factors. Propofol reduced inflammation by up-regulating miR-223-3p, thereby reducing POCD in aged rats.

P38-TFEB pathways promote microglia activation through inhibiting CMA-mediated NLRP3 degradation in Parkinson's disease

BackgroundParkinson’s disease (PD) is characterized by degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc), accompanied by accumulation of α-synuclein, chronic neuroinflammation and autophagy dysfunction. Previous studies suggested that misfolded α-synuclein induces the inflammatory response and autophagy dysfunction in microglial cells. The NLRP3 inflammasome signaling pathway plays a crucial role in the neuroinflammatory process in the central nervous system. However, the relationship between autophagy deficiency and NLRP3 activation induced by α-synuclein accumulation is not well understood.MethodsThrough immunoblotting, immunocytochemistry, immunofluorescence, flow cytometry, ELISA and behavioral tests, we investigated the role of p38-TFEB-NLRP3 signaling pathways on neuroinflammation in the α-synuclein A53T PD models.ResultsOur results showed that increased protein levels of NLRP3, ASC, and caspase-1 in the α-synuclein A53T PD models. P38 is activated by overexpression of α-synuclein A53T mutant, which inhibited the master transcriptional activator of autophagy TFEB. And we found that NLRP3 was degraded by chaperone-mediated autophagy (CMA) in microglial cells. Furthermore, p38-TFEB pathways inhibited CMA-mediated NLRP3 degradation in Parkinson's disease. Inhibition of p38 had a protective effect on Parkinson's disease model via suppressing the activation of NLRP3 inflammasome pathway. Moreover, both p38 inhibitor SB203580 and NLRP3 inhibitor MCC950 not only prevented neurodegeneration in vivo, but also alleviated movement impairment in α-synuclein A53T-tg mice model of Parkinson’s disease.ConclusionOur research reveals p38-TFEB pathways promote microglia activation through inhibiting CMA-mediated NLRP3 degradation in Parkinson's disease, which could be a potential therapeutic strategy for PD.Graphical abstractp38-TFEB pathways promote microglia activation through inhibiting CMA-mediated NLRP3 degradation in Parkinson's disease. In this model, p38 activates NLRP3 inflammasome via inhibiting TFEB in microglia. TFEB signaling negatively regulates NLRP3 inflammasome through increasing LAMP2A expression, which binds to NLRP3 and promotes its degradation via chaperone-mediated autophagy (CMA). NLRP3-mediated microglial activation promotes the death of dopaminergic neurons.

PDCD4 Simultaneously Promotes Microglia Activation via PDCD4-MAPK-NF-κB Positive Loop and Facilitates Neuron Apoptosis During Neuroinflammation.

Neuroinflammation and neuron injury are common features of the central nervous system (CNS) diseases. It is of great significance to identify their shared key regulatory molecules and thus explore the potential therapeutic targets. Programmed cell death factor 4 (PDCD4), an apoptosis-related molecule, extensively participates in tumorigenesis and inflammatory diseases, but its expression and biological function during CNS neuroinflammation remain unclear. In the present study, utilizing the lipopolysaccharide (LPS)-induced neuroinflammation model in mice, we reported an elevated expression of PDCD4 both in injured neurons and activated microglia of the inflamed brain. A similar change in PDCD4 expression was observed in vitro in the microglial activation model. Silencing PDCD4 by shRNA significantly inhibited the phosphorylation of MAPKs (p38, ERK, and JNK), prevented the phosphorylation and nuclear translocation of NF-κB p65, and thus attenuated the LPS-induced microglial inflammatory activation. Interestingly, LPS also required the MAPK/NF-κB signaling activation to boost PDCD4 expression in microglia, indicating the presence of a positive loop. Moreover, a persistent elevation of PDCD4 expression was detected in the H2O2-induced neuronal oxidative damage model. Knocking down PDCD4 significantly inhibited the expression of pro-apoptotic proteins BAX and Cleaved-PARP, suggesting the proapoptotic activity of PDCD4 in neurons. Taken together, our data indicated that PDCD4 may serve as a hub regulatory molecule that simultaneously promotes the microglial inflammatory activation and the oxidative stress-induced neuronal apoptosis within CNS. The microglial PDCD4-MAPK-NF-κB positive feedback loop may act as pivotal signaling for neuroinflammation which subsequently exaggerates neuronal injury, and thus may become a potential therapeutic target for neuroinflammatory diseases.

Agonist of growth hormone–releasing hormone enhances retinal ganglion cell protection induced by macrophages after optic nerve injury

Optic neuropathies are leading causes of irreversible visual impairment and blindness, currently affecting more than 100 million people worldwide. Glaucoma is a group of optic neuropathies attributed to progressive degeneration of retinal ganglion cells (RGCs). We have previously demonstrated an increase in survival of RGCs by the activation of macrophages, whereas the inhibition of macrophages was involved in the alleviation on endotoxin-induced inflammation by antagonist of growth hormone-releasing hormone (GHRH). Herein, we hypothesized that GHRH receptor (GHRH-R) signaling could be involved in the survival of RGCs mediated by inflammation. We found the expression of GHRH-R in RGCs of adult rat retina. After optic nerve crush, subcutaneous application of GHRH agonist MR-409 or antagonist MIA-602 promoted the survival of RGCs. Both the GHRH agonist and antagonist increased the phosphorylation of Akt in the retina, but only agonist MR-409 promoted microglia activation in the retina. The antagonist MIA-602 reduced significantly the expression of inflammation-related genes Il1b, Il6, and Tnf Moreover, agonist MR-409 further enhanced the promotion of RGC survival by lens injury or zymosan-induced macrophage activation, whereas antagonist MIA-602 attenuated the enhancement in RGC survival. Our findings reveal the protective effect of agonistic analogs of GHRH on RGCs in rats after optic nerve injury and its additive effect to macrophage activation, indicating a therapeutic potential of GHRH agonists for the protection of RGCs against optic neuropathies especially in glaucoma.

Effects of lead exposure on the activation of microglia in mice fed with high-fat diets.

Lead (Pb) exposure can cause central nervous system (CNS) damage. The process of Pb neurotoxicity is accompanied by the microglia activation. In addition, microglia activation was observed under the intervention of high-fat diets (HFD). This study was designed to investigate the effect of Pb on the cognitive function of mice with HFD, with focus on the microglia activation in brain. Male C57BL/6J mice, 8 weeks of age, were randomly divided into control, HFD, Pb, and HFD + Pb groups. The results showed that HFD following Pb exposure could exacerbate the learning and memory impairment in mice. Pb exposure could promote microglia activation and increase the expression of M1 microglia marker and decrease the expression of M2 microglia marker in the hippocampus of mice with HFD. Our finding suggested that Pb exposure may aggravate CNS damage by promoting M1 polarization and inhibiting M2 polarization of hippocampal microglia in HFD mice.

Concurrent microglial activation in CD8 T cell-mediated CNS vasculature permeability during Theiler’s virus infection

Abstract Immune-mediated blood brain barrier (BBB) disruption is a prominent feature of various neurological conditions for which an emerging role of CD8 T cells is being realized. Our group has developed a unique model of CD8 T cell-mediated BBB disruption which employs Theiler’s murine encephalomyelitis virus (TMEV) infection. Upon intravenous administration of VP2121–130 viral peptide during the peak antiviral adaptive response, Db:VP2121–130 epitope specific CD8 T cells induce BBB disruption in a perforin dependent manner. In this model, we addressed the role of microglia in relation to antigen specific CD8+ T cells and permeable cerebral vessels. Using real time two-photon in vivo imaging, we demonstrate that microglia adopt distinct morphological features, including enlarged cell body and fewer ramified processes as early as 6 hours post administration of VP2 peptide. Notably, microglial population exhibit robust down-regulation of homeostatic markers including CX3CR1 during BBB disruption. This study demonstrates CD8 T cells can promote microglia activation in a perforin-dependent manner during BBB disruption. Importantly, microglial activation occurs concurrently with the onset of vascular permeability and could serve as a critical cell type in this process.

Serum Exosomal microRNA-27-3p Aggravates Cerebral Injury and Inflammation in Patients with Acute Cerebral Infarction by Targeting PPARγ.

Acute cerebral infarction (ACI) possesses high mortality. Exosomes present in serum have potential application value in ACI diagnosis. This study investigated the mechanism of serum exosomes in ACI. Serum exosomes isolated from ACI patients and normal people were identified and then injected into the established middle cerebral artery occlusion (MCAO) rat model to evaluate cerebral injury and inflammation. Exosomal microRNA (miR)-27-3p expression was detected and interfered to analyze rat cerebral inflammation. The binding relationship between miR-27-3p and PPARγ was predicted and verified. The lipopolysaccharide (LPS)-treated microglia model was established and intervened with miR-27-3p to detect PPARγ, Iba-1, and inflammation-related factor expressions. After overexpressing PPARγ, rat cerebral inflammation was evaluated. The clinical significance of serum exosomal miR-27-3p in ACI was evaluated. Serum exosomes from ACI patients caused exacerbated MCAO rat cerebral injury and poor behavior recovery, as well as promoted cerebral inflammation. Serum exosomal miR-27-3p deepened rat brain inflammation. miR-27-3p targeted PPARγ to promote microglia activation and inflammation-related factor expressions in MCAO rats, and overexpressing PPARγ attenuated MCAO rat cerebral inflammation. Serum exosomal miR-27-3p promised to be a biomarker for ACI. We proved that serum exosomes from ACI patients aggravated ACI patient cerebral inflammation via the miR-27-3p/PPARγ axis.

LncRNA-Meg3 promotes Nlrp3-mediated microglial inflammation by targeting miR-7a-5p

Recent studies have identified neuroinflammation as a significant contributor to the pathological process of traumatic brain injury (TBI) and as a potentially effective target for treatment. LncRNA maternally expressed gene 3 (Meg3) has further been observed to play a critical role in diverse biological processes, including microglial activation and the inflammatory response. However, its target gene and associated signaling pathway require further elucidation. This study found that lipopolysaccharide + ATP upregulated Meg3, promoted microglia activation, Nlrp3/caspase1 activation and inflammation, and markedly reduced miR-7a-5p. Overexpression of miR-7a-5p attenuated Meg3-induced microglial activation, but not Meg3 expression. Bioinformatic analysis and dual-luciferase assays indicated that Meg3 was a direct target of miR-7a-5p that negatively regulates miR-7a-5p expression. Further, we showed that Meg3 acted as a competing endogenous RNA for miR-7a-5p and induced microglial inflammation by regulating nod-like receptor protein 3 (Nlrp3) expression. Our study thus demonstrates Meg3 regulates microglia inflammation by targeting the miR-7a-5p /Nlrp3 pathway.

MiR-497 promotes microglia activation and proinflammatory cytokines production in chronic unpredictable stress-induced depression via targeting FGF2

Depression is one of important prevalent psychiatric disorders worldwide. MiR-497 is considered as a diagnostic biomarker and a promising therapeutic target in cancers. However, the role of miR-497 in depression remains unknown. In this study, we demonstrated that CUS induced depression-like behaviors and overexpression of miR-497 in rats. Interestingly, knockdown miR-497 ameliorated CUS-induced depressive-like behavior in rats. Moreover, knockdown of miR-497 inhibited the activation of microglia and the production of proinflammatory cytokines including IL-6, IL-1β, MCP-1 and TNF-α in CUS-induced rats. Luciferase activity assay proved that Fibroblast Growth Factor-2 (FGF2) was a direct target of miR-497 and modulated by miR-497 in microglia. In rescue experiments, overexpression of FGF2 inhibited miR-497-induced proinflammatory cytokines and iNOS expression. These results showed that miR-497 aggravated hippocampal microglial activation in CUS-induced depression in rat via targeting FGF2, providing a novel potential target for treatment of depression.