Microglial Polarization Research Articles

Human microglia polarization following infection with the Lyme disease spirochete.

Infection with Borrelia burgdorferi can spread and cause central nervous system involvement, known as neuroborreliosis. Microglia phagocytose bacteria, mediate inflammation, and elicit an immune response toward the spirochete. Like other tissue macrophages, microglia can polarize into two different modulatory phenotypes, M1 and M2. We explored human microglial polarization changes upon infection with B. burgdorferi. HMC3 human microglia cell line was infected with B. burgdorferi for 24 h. Expression of polarization markers was evaluated via flow cytometry at 4 and 24 h. Secreted immunological mediators were evaluated using a multiplex ELISA system at 4, 18, and 24 h. An early decrease followed by a later increase in expression of M1 polarization marker iNOS was observed at 4 h, and 24 h, respectively. A decrease in M2 marker CX3CR1 occurred at 24 h. There were no changes in expression of M1 markers CD14, or in M2 markers CD163 and CD206. Multiplex ELISA evidenced an increase in secretion of activation markers MIP-1α, MIP- 1β, IP-10, chemotactic factor MCP-1, M1 polarization cytokine IL-8, and VEGF, at 4, 18, and 24 h. A decrease of iNOS at 4 h of infection suggests a diminished production of reactive nitrogen species that are a critical component of innate defense against infection. Increased iNOS and simultaneously decreased expression of CX3CR1 at 24 h, may suggest initiation of neuroprotective regulation of microglia recruitment to neuroinflammation. The dynamics of major inflammatory cytokines appear to be important in the microglial response to B. burgdorferi and should be further studied as these could become therapeutic targets in neuroborreliosis.

Oxygen Glucose Deprivation-Induced Lactylation of H3K9 Contributes to M1 Polarization and Inflammation of Microglia Through TNF Pathway.

Hypoxia-induced M1 polarization of microglia and resultant inflammation take part in the damage caused by hypoxic-ischemic encephalopathy (HIE). Histone lactylation, a novel epigenetic modification where lactate is added to lysine residues, may play a role in HIE pathogenesis. This study investigates the role of histone lactylation in hypoxia-induced M1 microglial polarization and inflammation, aiming to provide insights for HIE treatment. In this study, we assessed the effects of hypoxia on microglial polarization using both an HIE animal model and an oxygen-glucose deprivation cell model. Histone lactylation at various lysine residues was detected by Western blotting. Microglial polarization and inflammatory cytokines were analyzed by immunofluorescence, qPCR, and Western blotting. RNA sequencing, ChIP-qPCR, and siRNA were used to elucidate mechanisms of H3K9 lactylation. H3K9 lactylation increased due to cytoplasmic lactate during M1 polarization. Inhibiting P300 or reducing lactate dehydrogenase A expression decreased H3K9 lactylation, suppressing M1 polarization. Transcriptomic analysis indicated that H3K9 lactylation regulated M1 polarization via the TNF signaling pathway. ChIP-qPCR confirmed H3K9 lactylation enrichment at the TNFα locus, promoting OGD-induced M1 polarization and inflammation. H3K9 lactylation promotes M1 polarization and inflammation via the TNF pathway, identifying it as a potential therapeutic target for neonatal HIE.

Soluble Epoxide Hydrolase Inhibitor Ameliorates Olfactory Dysfunction, Modulates Microglia Polarization, and Attenuates Neuroinflammation after Ischemic Brain Injury.

Olfactory bulb (OB) microglia activation and inflammation can lead to olfactory dysfunction, which often occurs after an ischemic stroke. Inhibition of soluble epoxide hydrolase (sEH) attenuates neuroinflammation in brain injuries by reducing the degradation of anti-inflammatory epoxyeicosatrienoic acids. However, whether sEH inhibitors can ameliorate olfactory dysfunction after an ischemic stroke remains unknown. Ischemic brain injury and olfactory dysfunction were induced by middle cerebral artery occlusion (MCAO) in Wistar Kyoto rats. The rats were administered 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA), a selective sEH inhibitor. Olfactory function, cerebral infarct volume, and the degree of degeneration, microglial polarization and neuroinflammation in OB were evaluated. Following treatment with AUDA, rats subjected to MCAO displayed mild cerebral infarction and OB degeneration, as well as better olfactory performance. In OB, AUDA triggered a modulation of microglial polarization toward the M2 anti-inflammatory type, reduction in proinflammatory mediators, and enhancement of the antioxidant process. The effectiveness of AUDA in terms of anti-inflammatory, neuroprotection and anti-oxidative properties suggests that it may have clinical therapeutic implication for ischemic stroke related olfactory dysfunction.

Ischemia-induced endogenous Nrf2/HO-1 axis activation modulates microglial polarization and restrains ischemic brain injury.

Cerebral ischemic stroke accounts for more than 80% of all stroke cases. During cerebral ischemia, reactive oxygen species produced in the ischemic brain induce oxidative stress and inflammatory responses. Nrf2 is a transcription factor responsible for regulating cellular redox balance through the induction of protective antioxidant and phase II detoxification responses. Although the induction of endogenous Nrf2/HO-1 axis activation has been observed in the ischemic brain, whether ischemia-induced endogenous Nrf2/HO-1 axis activation plays a role in modulating microglia (MG) phenotypes and restraining ischemic brain injury is not characterized and requires further exploration. To investigate that, we generated mice with Nrf2 knockdown specifically in MG to rigorously assess the role of endogenous Nrf2 activation in ischemic brain injury after stroke. Our results showed that MG-specific Nrf2 knockdown exacerbated ischemic brain injury after stroke. We found that Nrf2 knockdown altered MG phenotypes after stroke, in which increased frequency of inflammatory MG and decreased frequency of anti-inflammatory MG were detected in the ischemic brain. Moreover, we identified attenuated Nrf2/HO-1 axis activation led to increased CD68/IL-1β and suppressed CD206 expression in MG, resulting in aggravated inflammatory MG in MG-specific Nrf2 knockdown mice after stroke. Intriguingly, using type II diabetic preclinical models, we revealed that diabetic mice exhibited attenuated Nrf2/HO-1 axis activation in MG and exacerbated ischemic brain injury after stroke that phenocopy mice with MG-specific Nrf2 knockdown. Finally, the induction of exogenous Nrf2/HO-1 axis activation in MG through pharmacological approaches ameliorated ischemic brain injury in diabetic mice. In conclusion, our findings provide cellular and molecular insights demonstrating ischemia-induced endogenous Nrf2/HO-1 axis activation modulates MG phenotypes and restrains ischemic brain injury. These results further strengthen the therapeutic potential of targeting Nrf2/HO-1 axis in MG for the treatment of ischemic stroke and diabetic stroke.

HDAC Inhibitors recapitulate Human Disease-Associated Microglia Signatures in vitro.

Disease-associated microglia (DAM), initially described in mouse models of neurodegenerative diseases, have been classified into two related states; starting from a TREM2-independent DAM1 state to a TREM2 dependent state termed DAM2, with each state being characterized by the expression of specific marker genes 1 . Recently, single-cell (sc)RNA-Seq studies have reported the existence of DAMs in humans 2-6 ; however, whether DAMs play beneficial or detrimental roles in the context of neurodegeneration is still under debate 7,8 . Here, we present a pharmacological approach to mimic human DAM in vitro by exposing different human microglia models to selected histone deacetylase (HDAC) inhibitors. We also provide an initial functional characterization of our model system, showing a specific increase of amyloid beta phagocytosis along with a reduction of MCP-1 secretion. Additionally, we report an increase in MITF expression, a transcription factor previously described to drive expression towards the DAM phenotype. We further identify CADM1 , LIPA and SCIN as DAM- marker genes shared across various proposed DAM signatures and in our model systems. Overall, our strategy for targeted microglial polarization bears great potential to further explore human DAM function and biology.

Intranasal Delivery of Pure Nanodrug Loaded Liposomes for Alzheimer's Disease Treatment by Efficiently Regulating Microglial Polarization.

The activated M1-like microglia induced neuroinflammation is the critical pathogenic event in Alzheimer's disease (AD). Microglial polarization from pro-inflammatory M1 toward anti-inflammatory M2 phenotype is a promising strategy. To efficiently accomplish this, amyloid-β (Aβ) aggregates as the culprit of M1 microglia activation should be uprooted. Interestingly, this study finds out that the self-reassembly of curcumin molecules into carrier-free curcumin nanoparticles (CNPs) exhibits multivalent binding with Aβ to achieve higher inhibitory effect on Aβ aggregation, compared to free curcumin with monovalent effect. Based on this, the CNPs loaded cardiolipin liposomes are developed for efficient microglial polarization. After intranasal administration, the liposomes decompose to release CNPs and cardiolipin in response to AD oxidative microenvironment. The CNPs inhibit Aβ aggregation and promote Aβ phagocytosis/clearance in microglia, removing roadblock to microglial polarization. Subsequently, CNPs are endocytosed by microglia and inhibit TLR4/NF-κB pathway for microglia polarization (M1→M2). Meanwhile, cardiolipin is identified as signaling molecule to normalize microglial dysfunction to prevent pro-inflammatory factors release. In AD transgenic mice, neuroinflammation, Aβ burden, and memory deficits are relieved after treatment. Through combined attack by extracellularly eradicating roadblock of Aβ aggregation and intracellularly inhibiting inflammation-related pathways, this nanotechnology assisted delivery system polarizes microglia efficiently, providing a reliable strategy in AD treatment.

Electroacupuncture pretreatment inhibits the TLR4/NF-κB/TXNIP/NLRP3 signaling pathway and modulates microglial polarization to alleviate cerebral ischemia-reperfusion injury in rats

Cerebral ischemia–reperfusion injury is frequently associated with neuroinflammation. The modulation of microglial polarization presents a promising approach for addressing cerebral ischemia–reperfusion injury. While electroacupuncture preconditioning has demonstrated efficacy in the management of ischemic stroke, the underlying therapeutic mechanisms remain inadequately understood. The investigation focused on elucidating the relationship between alterations in the TLR4/NF-κB/TXNIP/NLRP3 signaling pathway and microglial polarization subsequent to EA pretreatment. Established a middle cerebral artery occlusion (MCAO) rat model following electroacupuncture (EA) treatment at the Baihui (GV 20) acupoint. Male Sprague-Dawley rats were randomly assigned to the sham, Ischemia/Reperfusion (I/R), I/R + EA groups (n = 6). The results of Nissl Staining and TUNEL Stainingl showed that the number of curative neurons increased significantly after pretreatment, indicating an improvement in neuron formation and an increase in the number of austenite. The level of apoptosis in brain tissue in the I/R group was significantly higher than that in the sham operation group. Electroacupuncture pretreatment can effectively inhibit apoptosis occurrence. In addition, electric acupuncture pretreatment protects rat blood–brain barrier integrity and mitochondrial function. After treatment, the number of M1-type microglia decreased, while the number of M2-type microglia increased. These results suggest that EA preconditioning may alleviate neurological deficits and neuronal apoptosis caused by cerebral I/R injury, while maintaining the integrity of the blood–brain barrier and promoting microglial polarization through the TLR4/NF-κB/TXNIP/NLRP3 signaling pathway. Our findings establish a new molecular mechanism and theoretical foundation for electroacupuncture therapy of ischemic stroke.

Neuroprotective effects of all-trans-retinoic acid are mediated via downregulation of TLR4/NF-κB signaling in a rat model of middle cerebral artery occlusion.

To determine the effects of all-trans-retinoic acid (ATRA) on the post-stroke inflammatory response and elucidate the underlying molecular mechanisms. This animal experiment was conducted at Central Laboratory, the First Affiliated Hospital of Guangdong Pharmaceutical University, Guangzhou, China during 2020-2022. Sprague-Dawley rats were subjected to middle cerebral artery occlusion (MCAO) for 1.5h, and treated with ATRA at 2 and 24h after reperfusion. Neurological deficit scores on behavioral tests, and cerebral infarct volume, microglial polarization, and the expression levels of inflammatory cytokines and proteins associated with TLR4/NF-κB signaling were assessed. The ATRA administration reduced cerebral infarct volume and ameliorated neurological deficit scores in MCAO rats. Additionally, ATRA relieved cerebral edema and downregulated the secretion of proinflammatory cytokines after stroke. Finally, ATRA attenuated the polarization of the microglia toward the M1 phenotype and promoted the activation of the beneficial M2 phenotype; the underlying mechanism potentially involved the suppression of the TLR4/NF-κB signaling pathway. The ATRA treatment promoted functional recovery in an experimental model of ischemic stroke by attenuating neural inflammation. ATRA potentially modulated microglia-mediated neuroinflammation via the downregulation of the TLR4/NF-κB signaling pathway, which makes it a candidate treatment for post-stroke neuroinflammation.

Endothelial pyroptosis-driven microglial activation in choroid plexus mediates neuronal apoptosis in hemorrhagic stroke rats

BackgroundSpontaneous intracerebral hemorrhage (ICH) is associated with alarmingly high rates of disability and mortality, and current therapeutic options are suboptimal. A critical component of ICH pathology is the initiation of a robust inflammatory response, often termed “cytokine storm,” which amplifies the secondary brain injury following the initial hemorrhagic insult. The precise sources and consequences of this cytokine-driven inflammation are not fully elucidated, necessitating further investigation. MethodsTo address this knowledge gap, our study conducted a comprehensive cytokine profiling using Luminex® assays, assessing 23 key cytokines. We then employed single-cell RNA sequencing and spatial transcriptomics at three critical time points post-ICH: the hyperacute, acute, and subacute phases. Integrating these multimodal analyses allowed us to identify the cellular origins of cytokines and elucidate their mechanisms of action. ResultsLuminex® cytokine assays revealed a significant upregulation of IL-6 and IL-1β levels at the 24-h post-ICH time point. Through the integration of scRNA-seq and spatial transcriptomics in the hemorrhagic hemisphere of rats, we observed a pronounced activation of cytokine-related signaling pathways within the choroid plexus. Initially, immune cell presence was sparse, but it surged 24 h post-ICH, particularly in the choroid plexus, indicating a substantial shift in the immune microenvironment. We traced the source of IL-1β and IL-6 to endothelial cells, establishing a link to pyroptosis. Endothelial pyroptosis post-ICH induced the production of IL-1β and IL-6, which activated microglial polarization characterized by elevated expression of Msr1, Lcn2, and Spp1 via the NF-κB pathway in the choroid plexus. Furthermore, we identified neuronal populations undergoing apoptosis, mediated by the Lcn2-SLC22A17 pathway in response to IL-1β and IL-6 signaling. Notably, the inhibition of pyroptosis using VX-765 significantly mitigated neurological impairments. ConclusionsOur study provides evidence that endothelial pyroptosis, characterized by the release of IL-1β and IL-6, triggers microglial polarization through NF-κB pathway activation, ultimately leading to microglia-mediated neuronal apoptosis in the choroid plexus post-ICH. These findings suggest that targeted therapeutic strategies aimed at mitigating endothelial cell pyroptosis and neutralizing inflammatory cytokines may offer neuroprotection for both microglia and neurons, presenting a promising avenue for ICH treatment.

Regulation of microglia inflammation and oligodendrocyte demyelination by Engeletin via the TLR4/RRP9/NF-κB pathway after spinal cord injury

Microglia polarization is crucial for neuroinflammatory response after spinal cord injury (SCI). Small molecule compounds and hub genes play an important role in regulating microglia polarization, reducing neuroinflammatory response and oligodendrocyte demyelination after SCI. In this study, suitable data sets were used to screen hub genes, and Western blot and Immunofluorescence (IF) experiments were used to confirm the expressions of proteins related to SDAD1, RRP9 and NF-κB pathways under LPS/SCI conditions. Engeletin (ENG) reduced microglia polarization and inflammation in vivo and in vitro via the SDAD1, RRP9 or NF-κB signaling pathways. In addition, ENG binds to the membrane receptor Toll-like receptor 4 (TLR4) through small molecule-protein docking. COIP experiment and protein-protein docking revealed protein-protein interaction (PPI) between RRP9 and SDAD1. By gene knock-down (KD) / overexpression (OE) and Western blot experiments, RRP9 and SDAD1 can regulate inflammatory response through NF-κB signaling and ribosome biogenesis pathway. Western blot analysis showed that CU increased the expression of SDAD1, RRP9 and NF-κB pathway related proteins through TLR1/2, while C34 decreased the expression of SDAD1 and RRP9 proteins through TLR4. These results suggest that ENG can reduce inflammation through TLR4/RRP9(SDAD1)/NF-κB signaling pathway. In addition, we demonstrated that oligodendrocyte apoptosis and demyelination could be influenced by the regulation of microglia and tissue inflammation. In conclusion, this study found the gene Rrp9/Sdad1 and the small molecule compound ENG, which control the inflammatory response of microglia, and further explored the related mechanism of oligodendrocyte demyelination, which has important theoretical significance.

Changes in Type 1 Diabetes-Associated Gut Microbiota Aggravate Brain Ischemia Injury by Affecting Microglial Polarization Via the Butyrate-MyD88 Pathway in Mice.

People with type 1 diabetes (T1D) have a significantly elevated risk of stroke, but the mechanism through which T1D worsens ischemic stroke remains unclear. This study was aimed at investigating the roles of T1D-associated changes in the gut microbiota in aggravating ischemic stroke and the underlying mechanism. Fecal 16SrRNA sequencing indicated that T1D mice and mice with transplantation of T1D mouse gut microbiota had lower relative abundance of butyric acid producers, f_Erysipelotrichaceae and g_Allobaculum, and lower content of butyric acid in feces. After middle cerebral artery occlusion (MCAO), these mice had poorer neurological outcomes and more severe inflammation, but higher expression of myeloid differentiation factor 88 (MyD88) in the ischemic penumbra; moreover, the microglia were inclined to polarize toward the pro-inflammatory type. Administration of butyrate to T1D mice in the drinking water alleviated the neurological damage after MCAO. Butyrate influenced the response and polarization of BV2 and decreased the production of inflammatory cytokines via MyD88 after oxygen-glucose deprivation/reoxygenation. Knocking down MyD88 in the brain alleviated neurological outcomes and decreased the concentrations of inflammatory cytokines in the brain after stroke in mice with transplantation of T1D mouse gut microbiota. Poor neurological outcomes and aggravated inflammatory responses of T1D mice after ischemic stroke may be partly due to differences in microglial polarization mediated by the gut microbiota-butyrate-MyD88 pathway. These findings provide new ideas and potential intervention targets for alleviating neurological damage after ischemic stroke in T1D.

Neuroprotective effects of Gastrodia elata Blume on promoting M2 microglial polarization by inhibiting JNK/TLR4/T3JAM/NF-κB signaling after transient ischemic stroke in rats.

Gastrodia elata Blume, also called Tian Ma (TM), has been used to treat stroke for centuries. However, its effects on inflammation in acute cerebral ischemic injury and underlying mechanisms involved in microglial polarization remain unknown. The present study explored the effects of the TM extract on the modulation of microglial M1/M2 polarization 2days after transient cerebral ischemia. Male Sprague Dawley rats were intracerebroventricularly administered with 1% dimethyl sulfoxide 25min before cerebral ischemia and subsequently intraperitoneally administered 0.25g/kg (DO + TM-0.25g), 0.5g/kg (DO + TM-0.5g), or 1g/kg (DO + TM-1g) of the TM extract after cerebral ischemia onset. DO + TM-0.5g and DO + TM-1 g treatments downregulated the following: phospho-c-Jun N-terminal kinase (p-JNK)/JNK, tumor necrosis factor (TNF) receptor-associated factor 3 (TRAF3), TRAF3-interacting JNK-activating modulator (T3JAM), p-nuclear factor-kappa B p65 (p-NF-κB p65)/NF-κB p65, ionized calcium-binding adapter molecule 1 (Iba1), CD86, TNF-α, interleukin (IL)-1β, and IL-6 expression and toll-like receptor 4 (TLR4)/Iba1, CD86/Iba1, and p-NF-κB p65/Iba1 coexpression. These treatments also upregulated IL-10, nerve growth factor, and vascular endothelial growth factor A expression and YM-1/2/Iba1 and IL-10/neuronal nuclei coexpression in the cortical ischemic rim. The JNK inhibitor SP600125 exerted similar treatment effects as the DO + TM-0.5g and DO + TM-1 g treatments. DO + TM-0.5g and DO + TM-1 g/kg treatments attenuate cerebral infarction by inhibiting JNK-mediated signaling. TM likely exerts the neuroprotective effects of promoting M1 to M2 microglial polarization by inhibiting JNK/TLR4/T3JAM/NF-κB-mediated signaling in the cortical ischemic rim 2days after transient cerebral ischemia.

Poria cocos Extract Alleviates tPA-Induced Hemorrhagic Transformation after Ischemic Stroke through Regulation of Microglia M1/M2 Phenotypes Polarization.

Delayed thrombolytic therapy with tissue plasminogen activator (tPA), the only FDA-approved drug for ischemic stroke, can cause catastrophic hemorrhagic transformation (HT) after ischemic stroke. However, it remains largely unknown how microglial polarization dynamically changes in HT. Poria cocos is a widely used functional edible fungus in Asia and has been used for more than 2000 years as a food and medicine in China. Our preliminary study found that P. cocos extract (PCE) significantly reduced the volume of cerebral infarction. We performed the effects of PCE on tPA-induced HT in rat models of autologous thromboembolism middle cerebral artery occlusion in vivo and BV-2 cells injured by oxygen-glucose deprivation/reperfusion in vitro. Hemorrhage test and triphenyltetrazolium chloride staining were performed to examine the efficiency of PCE. The expression level of proteins associated with microglia polarization was detected using Western blotting and immunofluorescence staining. Small interfering RNA transfection reveals the regulatory mechanism of PCE on microglia polarization. PCE plus tPA reduced hemorrhage and infarct volumes after ischemic stroke. During tPA-induced HT, M1 microglia increased over time from 3 days onward and remained high for at least 7 days, reaching the peak at 7 days, M2 microglia gradually increased after 3 days and continued to increase for at least 14 days. Furthermore, PCE inhibited the secretion of pro-inflammatory cytokines in M1 microglia and improved the secretion of anti-inflammatory cytokines in M2 microglia, which related to the regulation of the IRF5-IRF4 axis. This current study indicates that PCE alleviates tPA-induced HT after ischemic stroke by modulating microglia M1/M2 phenotype polarization.

High-dose dexamethasone regulates microglial polarization via the GR/JAK1/STAT3 signaling pathway after traumatic brain injury.

Although microglial polarization and neuroinflammation are crucial cellular responses after traumatic brain injury, the fundamental regulatory and functional mechanisms remain insufficiently understood. As potent anti-inflammatory agents, the use of glucocorticoids in traumatic brain injury is still controversial, and their regulatory effects on microglial polarization are not yet known. In the present study, we sought to determine whether exacerbation of traumatic brain injury caused by high-dose dexamethasone is related to its regulatory effects on microglial polarization and its mechanisms of action. In vitro cultured BV2 cells and primary microglia and a controlled cortical impact mouse model were used to investigate the effects of dexamethasone on microglial polarization. Lipopolysaccharide, dexamethasone, RU486 (a glucocorticoid receptor antagonist), and ruxolitinib (a Janus kinase 1 antagonist) were administered. RNA-sequencing data obtained from a C57BL/6 mouse model of traumatic brain injury were used to identify potential targets of dexamethasone. The Morris water maze, quantitative reverse transcription-polymerase chain reaction, western blotting, immunofluorescence and confocal microscopy analysis, and TUNEL, Nissl, and Golgi staining were performed to investigate our hypothesis. High-throughput sequencing results showed that arginase 1, a marker of M2 microglia, was significantly downregulated in the dexamethasone group compared with the traumatic brain injury group at 3 days post-traumatic brain injury. Thus dexamethasone inhibited M1 and M2 microglia, with a more pronounced inhibitory effect on M2 microglia in vitro and in vivo. Glucocorticoid receptor plays an indispensable role in microglial polarization after dexamethasone treatment following traumatic brain injury. Additionally, glucocorticoid receptor activation increased the number of apoptotic cells and neuronal death, and also decreased the density of dendritic spines. A possible downstream receptor signaling mechanism is the GR/JAK1/STAT3 pathway. Overactivation of glucocorticoid receptor by high-dose dexamethasone reduced the expression of M2 microglia, which plays an anti-inflammatory role. In contrast, inhibiting the activation of glucocorticoid receptor reduced the number of apoptotic glia and neurons and decreased the loss of dendritic spines after traumatic brain injury. Dexamethasone may exert its neurotoxic effects by inhibiting M2 microglia through the GR/JAK1/STAT3 signaling pathway.

Lacticaseibacillus rhamnosus KY16 Improves Depression by Promoting Intestinal Secretion of 5-HTP and Altering the Gut Microbiota.

Increasing research suggests a connection between gut microbiota and depressive disorders. Targeted changes to the intestinal flora may contribute to alleviating anxiety and depression. This study aimed to identify probiotics that could attenuate stress-induced abnormal behavior and explore potential mechanisms. The administration of LR.KY16 significantly reduced stress-induced abnormal behaviors and physiological dysfunction. The mechanism may be via regulating the structure of the intestinal microbiota in mice, increasing the abundance of Akkermansia muciniphila, prompting enterochromaffin cells to secrete 5-HTP in the gut, which enters the brain through the bloodstream and promotes the synthesis of 5-HT in the brain, and then activates brain-derived neurotrophic factor (BDNF)/tyrosine kinase receptor B (TrkB) through the 5-HT1A receptor. In addition, LR.KY16 also increased the expression of claudin-7, occludin, and zonula occludens-1 (ZO-1) in the colon, inhibited microglial M1 polarization, and inhibited systemic inflammation.

Role of TREM1 in the sevoflurane‐induced inflammatory activation of microglia in vitro

AbstractPerioperative neurocognitive disorders (PNDs) are one of the most common complications in perioperative patients, and neuroinflammatory reaction mediated by microglia plays a key role in their formation, but the underlying mechanism remains unknown. Given that the triggering receptor expressed on myeloid cells 1 (TREM1) is a key regulator of inflammation, this study aimed to observe the role of TREM1 on the sevoflurane‐induced inflammatory activation in microglia. BV2 microglia were subjected to varying sevoflurane concentrations and durations to assess their viability using CCK8 and the expression of TREM1, iNOS, and ARG using enzyme‐linked immunosorbent assays. Additionally, TREM1 knockdown lentivirus was employed to examine its impacts on microglia response to sevoflurane and altered expression of inflammatory markers, IL‐1β, TNF‐α, TGF‐β, IL‐10, iNOS, and ARG, as detected using qRT‐PCR and immunofluorescence for INOS/Iba‐1 and ARG/Iba‐1. Our findings underscore the potent inflammatory activation induced by prolonged, high‐concentration sevoflurane exposure on microglia. We highlight the potential role of TREM1 as a modulator of microglial polarization and a potential target for the treatment and prevention of sevoflurane‐induced PNDs.

MFG-E8 Ameliorates Nerve Injury-Induced Neuropathic Pain by Regulating Microglial Polarization and Neuroinflammation via Integrin β3/SOCS3/STAT3 Pathway in Mice.

Spinal microglial polarization plays a crucial role in the pathological processes of neuropathic pain following peripheral nerve injury. Accumulating evidence suggests that milk fat globule epidermal growth factor-8 (MFG-E8) exhibits anti-inflammatory effect and regulates microglial polarization through the integrin β3 receptor. However, the impact of MFG-E8 on microglial polarization in the context of neuropathic pain has not yet been investigated. In this study, we evaluated the effect of MFG-E8 on pain hypersensitivity and spinal microglial polarization following spared nerve injury (SNI) of the sciatic nerve in mice. We determined the molecular mechanisms underlying the effects of MFG-E8 on pain hypersensitivity and spinal microglial polarization using pain behavior assessment, western blot (WB) analysis, immunofluorescence (IF) staining, quantitative polymerase chain reaction (qPCR), enzyme-linked immunosorbent assay (ELISA), and small interfering RNA (siRNA) transfection. Our findings indicate that SNI significantly increased the levels of MFG-E8 and integrin β3 expressed in microglia within the spinal cord of mice. Additionally, we observed that intrathecal injection of recombinant human MFG-E8 (rhMFG-E8) alleviated SNI induced-mechanical allodynia and thermal hyperalgesia. Furthermore, the results suggested that rhMFG-E8 facilitated M2 microglial polarization and ameliorated neuroinflammation via integrin β3/SOCS3/STAT3 pathway in the spinal cord of mice with SNI. Importantly, these effects were negated by integrin β3 siRNA, or SOCS3 siRNA. These results demonstrate that MFG-E8 ameliorates peripheral nerve injury induced-mechanical allodynia and thermal hyperalgesia by driving M2 microglial polarization and mitigating neuroinflammation mediated by integrin β3/SOCS3/STAT3 pathway in the spinal cord of mice. MFG-E8 may serve as a promising target for the treatment of neuropathic pain.

Research Progress on Treating Spinal Cord Injury by Modulating the Phenotype of Microglia.

Spinal cord injury (SCI) is a severe central nervous system disorder with no currently available effective treatment. Microglia are immune cells in the central nervous system that play crucial roles in the SCI occurrence, development, and recovery stages. They exhibit dynamic polarization over time and can switch between classical activation (M1) and alternative activation (M2) phenotypes to respond to environmental stimuli. The M1 phenotype is involved in initiating and sustaining inflammatory responses, while the M2 phenotype exerts anti-inflammatory effects and promotes tissue repair in damaged areas. Inhibiting M1 polarization and promoting M2 polarization have become hotspots in regulating neuroinflammation and treating SCI. This article provides a comprehensive review centered on modulating microglial polarization phenotypes for SCI treatment.

Propofol alleviates M1 polarization and neuroinflammation of microglia in a subarachnoid hemorrhage model in vitro, by targeting the miR-140-5p/TREM-1/NF-κB signaling axis.

Subarachnoid hemorrhage (SAH) is a devastating stroke caused by ruptured intracranial aneurysms, leading to blood accumulation around the brain. Early brain injury (EBI) within 72 h post-SAH worsens prognosis, primarily due to intense neuroinflammation. Microglia, pivotal in central nervous system defense and repair, undergo M1 to M2 polarization post-SAH, with M1 exacerbating neuroinflammation. Propofol (PPF), an anesthetic with anti-inflammatory properties, shows promise in mitigating neuroinflammation in SAH by modulating microglial activation. It likely acts through microRNAs like miR-140-5p, which attenuates microglial activation and inflammation by targeting TREM-1 and the NF-κB pathway. Understanding these mechanisms could lead to new therapeutic approaches for SAH-related EBI. In this study, BV-2 cell was used to establish in vitro model of SAH, and the expression of miR-140-5p and TREM-1 was detected after modeling. Microglial activity, apoptosis, the inflammatory pathway and response, oxidative damage, and M1/M2 polarization of microglia were evaluated by drug administration or transfection according to experimental groups. Finally, the targeting relationship between miR-140-5p and TREM-1 was verified by dual luciferase reporter assays, and the effect of PPF on the miR-140-5p/TREM-1/NF-κB signaling cascade was evaluated by RT‒qPCR or Western blotting. PPF effectively mitigates apoptosis, neuroinflammation, oxidative damage, and M1 microglial polarization in SAH. In SAH cells, PPF upregulates miR-140-5p and downregulates TREM-1. Mechanistically, PPF boosts miR-140-5p expression, while TREM-1, a downstream target of miR-140-5p, inhibits NF-κB signaling by regulating TREM-1, promoting M1 to M2 microglial polarization. Reduced miR-140-5p or increased TREM-1 counters PPF's therapeutic impact on SAH cells. In conclusion, PPF plays a neuroprotective role in SAH by regulating the miR-140-5p/TREM-1/NF-κB signaling axis to inhibit neuroinflammation and M1 polarization of microglia.

Melatonin Induces Analgesic Effects through MT2 Receptor-Mediated Neuroimmune Modulation in the Mice Anterior Cingulate Cortex.

Neuropathic pain (NP) represents a considerable clinical challenge, profoundly impacting patients' quality of life. Presently, pharmacotherapy serves as a primary approach for NP alleviation, yet its efficacy often remains suboptimal. Melatonin (MLT), a biologically active compound secreted by the pineal gland, has long been associated with promoting and maintaining sleep. Although recent studies suggest analgesic effects of MLT, the underlying mechanism remains largely unknown, particularly its impact on the cortex. In this study, we induced an NP model in mice through spared nerve injury (SNI) and observed a considerable, dose-dependent alleviation in NP symptoms following intraperitoneal or anterior cingulate cortex (ACC) administration of MLT. Our findings further indicated that the NP management of MLT is selectively mediated by MLT-related receptor 2 (MT2R), rather than MT1R, on neurons and microglia within the ACC. Transcriptome sequencing, complemented by bioinformatics analysis, implicated MLT in the modulation of Gα(i) and immune-inflammatory signals. Specifically, MLT inhibited the excitability level of pyramidal cells in the ACC by activating the Gα(i) signaling pathway. Simultaneously, MLT attenuated M1 polarization and promoted M2 polarization of microglia, thereby mitigating the inflammatory response and type II interferon response within the ACC. These findings unveil a hitherto unrecognized molecular mechanism: an MLT-mediated neuroimmune modulation pathway in the ACC mediated by MT2R. This elucidation sheds light on the regulatory character of MLT in chronic nociceptive pain conditions, offering a prospective therapeutic strategy for NP management.