MFG-E8 Selectively Inhibited Aβ-Induced Microglial M1 Polarization via NF-κB and PI3K-Akt Pathways

MFG-E8 facilitates heart repair through M1/M2 polarization after myocardial infarction by inhibiting CaMKII

BACKGROUND

M1/M2 macrophage polarization affects patient outcomes after myocardial infarction (MI). The relationship between milk fat globule-epidermal growth factor 8 (MFG-E8) and Ca2+/calmodulin-dependent protein kinase II (CaMKII) on macrophage polarization after MI is unknown. To investigate the functional role of MFG-E8 in modulating cardiac M1/M2 macrophage polarization after MI, especially its influence on CaMKII signaling.

METHODS

Human ventricular tissue and blood were obtained from patients with MI and controls. MFG-E8-KO mice were constructed (C57BL/6). The mice were randomized to WT-sham, sham-MFG-E8-KO, WT-PBS, rmMFG-E8 (WT injected with rmMFG-E8 10 min after MI), and MFG-E8-KO. The mouse macrophage cell line RAW264.7 was obtained. CaMKII, p-CaMKII, Akt, and NF-κB p65 were determined by qRT-PCR, western blot, and immunofluorescence.

RESULTS

The MFG-E8 levels were significantly enhanced after MI in the hearts and plasma of patients with MI compared with controls. The MFG-E8 levels were significantly increased in the hearts and plasma of mice after MI. MFG-E8 was derived from cardiac fibroblasts. The administration of rmMFG-E8 improved ventricular remodeling and cardiac function after MI. rmMFG-E8 did not suppress infiltrating monocyte/macrophages into the peri-infarct area. rmMFG-E8 suppressed the polarization of macrophages to the M1 phenotype and promoted the polarization of macrophages to the M2 phenotype. rmMFG-E8 suppressed CaMKII-dependent signaling in macrophages.

CONCLUSIONS

MFG-E8 and CaMKII appear to collaboratively regulate myocardial remodeling and M1/M2 macrophage polarization after MI. These observations suggest new roles for MFG-E8 in inhibiting M1 but promoting M2 macrophage polarization.

Quercetin improves cerebral ischemia/reperfusion injury by promoting microglia/macrophages M2 polarization via regulating PI3K/Akt/NF-κB signaling pathway

The modulation of microglial polarization from the pro-inflammatory M1 to the anti-inflammatory M2 phenotype shows promise as a therapeutic strategy for ischemic stroke. Quercetin, a natural flavonoid abundant in various plants, possesses anti-inflammatory, anti-apoptotic, and antioxidant properties. Nevertheless, its effect and underlying mechanism on microglia/macrophages M1/M2 polarization in the treatment of cerebral ischemia/reperfusion injury (CI/RI) remain poorly explored. In the current study, we observed that quercetin ameliorated neurological deficits, reduced infarct volume, decreased the number of M1 microglia/macrophages (CD16/32+/Iba1+), and enhanced the number of M2 microglia/macrophages (CD206+/Iba1+) after establishing the CI/RI model in rats. Subsequent in vivo and in vitro experiments indicated that quercetin downregulated M1 markers (CD86, iNOS, TNF-α, IL-1β, and IL-6) and upregulated M2 markers (CD206, Arg-1, IL-10, and TGF-β). Network pharmacology analysis and molecular docking revealed that the PI3K/Akt/NF-κB signaling pathway emerged as the core pathway. Western blot confirmed that quercetin upregulated the phosphorylation of PI3K and Akt, while alleviating the phosphorylation of IκBα and NF-κB both in vivo and in vitro. However, the PI3K inhibitor LY294002 reversed the effects of quercetin on M2 polarization and the expression of key proteins in the PI3K/Akt/NF-κB pathway in primary microglia after oxygen-glucose deprivation/reoxygenation (OGD/R) in vitro. Collectively, our findings demonstrate that quercetin facilitates microglia/macrophages M2 polarization by modulating the PI3K/Akt/NF-κB signaling pathway in the treatment of CI/RI. These findings provide novel insights into the therapeutic mechanisms of quercetin in ischemic stroke.

Arterial Baroreflex Dysfunction Promotes Neuroinflammation by Activating the Platelet CD40L/Nuclear Factor Kappa B Signaling Pathway in Microglia and Astrocytes

Arterial baroreflex (ABR) dysfunction has previously been associated with neuroinflammation, the most common pathological feature of neurological disorders. However, the mechanisms mediating ABR dysfunction-induced neuroinflammation are not fully understood. In the present study, we investigated the role of platelet CD40 ligand (CD40L) in neuroinflammation in an in vivo model of ABR dysfunction, and microglia and astrocyte activation in vitro. ABR dysfunction was induced in Sprague‒Dawley rats by sinoaortic denervation (SAD). We used ELSA and immunofluorescence to assess the effect of platelet CD40L on glial cell polarization and the secretion of inflammatory factors. By flow cytometry, we found that rats subjected to SAD showed a high level of platelet microaggregation and upregulation of CD40L on the platelet surface. The promotion of platelet invasion and accumulation was also observed in the brain tissues of rats subjected to SAD. In the animal model and cultured N9 microglia/C6 astrocytoma cells, platelet CD40L overexpression promoted neuroinflammation and activated M1 microglia, A1 astrocytes, and the nuclear factor kappa B (NFκB) signaling pathway. These effects were partially blocked by inhibiting platelet activity with clopidogrel or inhibiting CD40L-mediated signaling. Our results suggest that during ABR dysfunction, CD40L signaling in platelets converts microglia to the M1 phenotype and astrocytes to the A1 phenotype, activating NFκB and resulting in neuroinflammation. Thus, our study provides a novel understanding of the pathogenesis of ABR dysfunction-induced neuroinflammation and indicates that targeting platelet CD40L is beneficial for treating central nervous system (CNS) disorders associated with ABR dysfunction.

Identification and antioxidative mechanism of novel mitochondria-targeted MFG-E8 polypeptides in virtual screening and in vitro study

Milk fat globule-EGF factor VIII (MFG-E8) has been identified as an important source of bioactive peptides, which may exert a pivotal role in regulating biologic redox equilibrium. However, the composition of MFG-E8 polypeptides and their mechanisms on mitigating sarcopenia remain unknown. The aim of this study was to identify the composition of MFG-E8 polypeptides and its effects against oxidative stress in dexamethasone-induced L6 cell injury. Simulated digestion in vitro and liquid chromatography-tandem mass spectrometry were used in this investigation. A total of 95 peptides were identified during complete simulated digestion; among them, the contents of 21 peptides were analyzed, having been determined to exceed 1%. Molecular docking assay found that IDLG, KDPG, YYR, and YYK exhibited high binding affinity with keap1. MTT, dichlorodihydrofluorescein diacetate, mito- and lyso-tracker, and transmission electron microscope assay demonstrated that IDLG and KDPG can alleviate oxidative stress-injured L6 cell vitality, mitochondria activity, vacuolation, and function decrease, and increased autophagy, thereby improving mitochondrial homeostasis. From a molecular perspective, IDLG and KDPG can decrease the expression of keap1 and increase the expression of Nrf2, HO-1, and PGC-1α. Therefore, MFG-E8-derived IDLG and KDPG could be potential polypeptides countering oxidative stress in the treatment of sarcopenia, via the keap1/Nrf2/HO-1 signaling pathway.

Phenylethanoid Glycosides of Cistanche Improve Learning and Memory Disorders in APP/PS1 Mice by Regulating Glial Cell Activation and Inhibiting TLR4/NF-κB Signaling Pathway

Phenylethanoid Glycosides of Cistanche (PhGs) have a certain curative effect on AD animal model, Echinacea (ECH) and verbascoside (ACT), as the quality control standard of Cistanche deserticola Y. C. Ma and the main representative compounds of PhGs have been proved to have neuroprotective effects, but the specific mechanism needs to be further explored. This study explored the mechanisms of PhGs, ECH, and ACT in the treatment of Alzheimer's disease (AD) from the perspectives of glial cell activation, TLR4/NF-κB signaling pathway, and synaptic protein expression. We used APP/PS1 mice as AD models. After treatment with PhGs, ECH, and ACT, the learning and memory abilities of APP/PS1 mice were enhanced, and the pathological changes in brain tissue were alleviated. The expression of pro-inflammatory M1 microglia markers (CD11b, iNOS, and IL-1β) was decreased; the expression of M2 microglia markers (Arg-1 and TGF-β1) was increased, which promoted the transformation of microglia from M1 pro-inflammatory phenotype to M2 anti-inflammatory phenotype. In addition, PhGs, ECH, and ACT could down-regulate the expression of proteins related to the TLR4/NF-κB signaling pathway and up-regulate the expression of synaptic proteins. The results indicated that PhGs, ECH, and ACT played a neuroprotective role by regulating the activation of glial cells and inhibiting the TLR4/NF-κB inflammatory pathway, and improving the expression levels of synapse-related proteins.

Schwann cell-derived exosomes containing MFG-E8 modify macrophage/microglial polarization for attenuating inflammation via the SOCS3/STAT3 pathway after spinal cord injury

Macrophage/microglia polarization acts as an important part in regulating inflammatory responses in spinal cord injury (SCI). However, the regulation of inflammation of Schwann cell-derived exosomes (SCDEs) for SCI repair is still unclear. Therefore, we intend to find out the effect of SCDEs on regulating the inflammation related to macrophage polarization during the recovery of SCI. Firstly, the thesis demonstrated that SCDEs could attenuate the LPS- inflammation in BMDMs by suppressing M1 polarization and stimulating M2 polarization. Similarly, SCDEs improved functional recovery of female Wistar rats of the SCI contusion model according to BBB (Basso, Beattie, and Bresnahan) score, electrophysiological assay, and the gait analysis system of CatWalk XT. Moreover, MFG-E8 was verified as the main component of SCDEs to improve the inflammatory response by proteomic sequencing and lentiviral transfection. Improvement of the inflammatory microenvironment also inhibited neuronal apoptosis. The knockout of MFG-E8 in SCs can reverse the anti-inflammatory effects of SCDEs treatment. The SOCS3/STAT3 signaling pathway was identified to participate in upregulating M2 polarization induced by MFG-E8. In conclusion, our findings will enrich the mechanism of SCDEs in repairing SCI and provide potential applications and new insights for the clinical translation of SCDEs treatment for SCI.

Immunomodulatory and Anti-inflammatory effect of Neural Stem/Progenitor Cells in the Central Nervous System

Neuroinflammation is a critical event that responds to disturbed homeostasis and governs various neurological diseases in the central nervous system (CNS). The excessive inflammatory microenvironment in the CNS can adversely affect endogenous neural stem cells, thereby impeding neural self-repair. Therapies with neural stem/progenitor cells (NSPCs) have shown significant inhibitory effects on inflammation, which is mainly achieved through intercellular contact and paracrine signalings. The intercellular contact between NSPCs and immune cells, the activated CNS- resident microglia, and astrocyte plays a critical role in the therapeutic NSPCs homing and immunomodulatory effects. Moreover, the paracrine effect mainly regulates infiltrating innate and adaptive immune cells, activated microglia, and astrocyte through the secretion of bioactive molecules and extracellular vesicles. However, the molecular mechanism involved in the immunomodulatory effect of NSPCs is not well discussed. This article provides a systematic analysis of the immunomodulatory mechanism of NSPCs, discusses efficient ways to enhance its immunomodulatory ability, and gives suggestions on clinical therapy.

Licochalcone E, a β-Amyloid Aggregation Inhibitor, Regulates Microglial M1/M2 Polarization via Inhibition of CTL1-Mediated Choline Uptake

Alzheimer's disease (AD) is thought to be a series of neuroinflammatory diseases caused by abnormal deposits of amyloid-β (Aβ) and tau protein in the brain as part of its etiology. We focused on Aβ aggregation and M1 and M2 microglial polarity in microglia to search for novel therapeutic agents. It has been reported that the inhibition of choline uptake via choline transporter-like protein 1 (CTL1) in microglia preferentially induces M2 microglial polarity. However, the role of the choline transport system on the regulation of microglial M1/M2 polarity in AD is not fully understood. Licochalcones (Licos) A-E, flavonoids extracted from licorice, have been reported to have immunological anti-inflammatory effects, and Lico A inhibits Aβ aggregation. In this study, we compared the efficacy of five Licos, from Lico A to E, at inhibiting Aβ1-42 aggregation. Among the five Licos, Lico E was selected to investigate the relationship between the inhibition of choline uptake and microglial M1/M2 polarization using the immortalized mouse microglial cell line SIM-A9. We newly found that Lico E inhibited choline uptake and Aβ1-42 aggregation in SIM-A9 cells in a concentration-dependent manner, suggesting that the inhibitory effect of Lico E on choline uptake is mediated by CTL1. The mRNA expression of tumor necrosis factor (TNF-α), a marker of M1 microglia, was increased by Aβ1-42, and its effect was inhibited by choline deprivation and Lico E in a concentration-dependent manner. In contrast, the mRNA expression of arginase-1 (Arg-1), a marker of M2 microglia, was increased by IL-4, and its effect was enhanced by choline deprivation and Lico E. We found that Lico E has an inhibitory effect on Aβ aggregation and promotes polarity from M1 to M2 microglia via inhibition of the CTL1 function in microglia. Thus, Lico E may become a leading compound for a novel treatment of AD.

RNA interference-mediated silencing of DNA methyltransferase 1 attenuates neuropathic pain by accelerating microglia M2 polarization

Background

DNA methyltransferase 1 (DNMT1) exerts imperative functions in neuropathic pain (NP). This study explored the action of RNA interference-mediated DNMT1 silencing in NP by regulating microglial M2 polarization.

Methods

NP rat models were established using chronic constriction injury (CCI) and highly aggressive proliferating immortalized (HAPI) microglia were treated with lipopolysaccharide (LPS) to induce microglia M1 polarization, followed by treatment of DNMT1 siRNA or si-DNMT1/oe-DNMT1, respectively. The pain threshold of CCI rats was assessed by determining mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL). Levels of inflammatory factors (TNF-α/IL-1β/IL-6/IL-10) and DNMT1 in rat L4-L6 spinal cord samples and HAPI cells were measured using ELISA, RT-qPCR, and Western blot. iNOS and Arg-1 mRNA levels were measured via RT-qPCR. DNMT1, M1 marker (iNOS), and M2 marker (Arg-1) levels in microglia of CCI rats were detected by immunofluorescence. Percentages of M1 microglia phenotype (CD16) and M2 microglia phenotype (CD206) were detected by flow cytometry. The phosphorylation of PI3K/Akt pathway-related proteins was determined by Western blot.

Results

CCI rats exhibited diminished MWT and TWL values, increased pro-inflammatory cytokines, and decreased anti-inflammatory cytokine IL-10. Additionally, DNMT1 was upregulated in CCI rat microglia. DNMT1 siRNA alleviated CCI-induced NP and facilitated M2 polarization of microglia in CCI rats. DNMT1 knockdown inhibited LPS-induced M1 polarization of HAPI cells and promoted M2 polarization by blocking the PI3K/Akt pathway, but DNMT1 overexpression inhibited the M1-to-M2 polarization of microglia.

Conclusion

RNA interference-mediated DNMT1 silencing accelerates microglia M2 polarization by impeding the PI3K/Akt pathway, thereby alleviating CCI-induced NP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02860-6.

C16 Peptide and Ang-1 Improve Functional Disability and Pathological Changes in an Alzheimer’s Disease Model Associated with Vascular Dysfunction

Alzheimer’s disease (AD) is a neurological disorder characterized by neuronal cell death, tau pathology, and excessive inflammatory responses. Several vascular risk factors contribute to damage of the blood–brain barrier (BBB), secondary leak-out of blood vessels, and infiltration of inflammatory cells, which aggravate the functional disability and pathological changes in AD. Growth factor angiopoietin-1 (Ang-1) can stabilize the endothelium and reduce endothelial permeability by binding to receptor tyrosine kinase 2 (Tie2). C16 peptide (KAFDITYVRLKF) selectively binds to integrin ανβ3 and competitively inhibits leukocyte transmigration into the central nervous system by interfering with leukocyte ligands. In the present study, 45 male Sprague-Dawley (SD) rats were randomly divided into three groups: vehicle group, C16 peptide + Ang1 (C + A) group, and sham control group. The vehicle and C + A groups were subjected to two-vessel occlusion (2-VO) with artery ligation followed by Aβ1-42 injection into the hippocampus. The sham control group underwent sham surgery and injection with an equal amount of phosphate-buffered saline (PBS) instead of Aβ1-42. The C + A group was administered 1 mL of drug containing 2 mg of C16 and 400 µg of Ang-1 daily for 2 weeks. The sham control and vehicle groups were administered 1 mL of PBS for 2 weeks. Our results showed that treatment with Ang-1 plus C16 improved functional disability and reduced neuronal death by inhibiting inflammatory cell infiltration, protecting vascular endothelial cells, and maintaining BBB permeability. The results suggest that these compounds may be potential therapeutic agents for AD and warrant further investigation.

Microglia Polarization From M1 to M2 in Neurodegenerative Diseases

Microglia-mediated neuroinflammation is a common feature of neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). Microglia can be categorized into two opposite types: classical (M1) or alternative (M2), though there’s a continuum of different intermediate phenotypes between M1 and M2, and microglia can transit from one phenotype to another. M1 microglia release inflammatory mediators and induce inflammation and neurotoxicity, while M2 microglia release anti-inflammatory mediators and induce anti-inflammatory and neuroprotectivity. Microglia-mediated neuroinflammation is considered as a double-edged sword, performing both harmful and helpful effects in neurodegenerative diseases. Previous studies showed that balancing microglia M1/M2 polarization had a promising therapeutic prospect in neurodegenerative diseases. We suggest that shifting microglia from M1 to M2 may be significant and we focus on the modulation of microglia polarization from M1 to M2, especially by important signal pathways, in neurodegenerative diseases.

Efferocytosis in multisystem diseases (Review)

Efferocytosis, the phagocytosis of apoptotic cells performed by both specialized phagocytes (such as macrophages) and non‑specialized phagocytes (such as epithelial cells), is involved in tissue repair and homeostasis. Effective efferocytosis prevents secondary necrosis, terminates inflammatory responses, promotes self‑tolerance and activates pro‑resolving pathways to maintain homeostasis. When efferocytosis is impaired, apoptotic cells that could not be cleared in time aggregate, resulting in the necrosis of apoptotic cells and release of pro‑inflammatory factors. In addition, defective efferocytosis inhibits the intracellular cholesterol reverse transportation pathways, which may lead to atherosclerosis, lung damage, non‑alcoholic fatty liver disease and neurodegenerative diseases. The uncleared apoptotic cells can also release autoantigens, which can cause autoimmune diseases. Cancer cells escape from phagocytosis via efferocytosis. Therefore, new treatment strategies for diseases related to defective efferocytosis are proposed. This review illustrated the mechanisms of efferocytosis in multisystem diseases and organismal homeostasis and the pathophysiological consequences of defective efferocytosis. Several drugs and treatments available to enhance efferocytosis are also mentioned in the review, serving as new evidence for clinical application.

Natural Products for Regulating Macrophages M2 Polarization

Macrophages M2 polarization have been taken as an anti-inflammatory progression during inflammation. Natural plant-derived products, with potential therapeutic and preventive activities against inflammatory diseases, have received increasing attention in recent years because of their whole regulative effects and specific pharmacological activities. However, the molecular mechanisms about how different kinds of natural compounds regulate macrophages polarization still unclear. Therefore, in the current review, we summarized the detailed research progress on the active compounds derived from herbal plants with regulating effects on macrophages, especially M2 polarization. These natural occurring compounds including flavonoids, terpenoids, glycosides, lignans, coumarins, alkaloids, polyphenols and quinones. In addition, we extensively discussed the cellular mechanisms underlying the M2 polarization for each compound, which could provide potential therapeutic strategies aiming macrophages M2 polarization.

TMT-based quantitative proteomics analysis reveals the effect of bovine derived MFG-E8 against oxidative stress on rat L6 cells

Sarcopenia is an aging-associated oxidative stress-induced mitochondrial dysfunction characterized by a decline in skeletal muscle mass, strength and function. Milk fat globule-EGF factor 8 (MFG-E8) is a secreted matrix glycoprotein that plays a crucial role in regulating tissue homeostasis and protecting against skeletal muscle injury. To explore the molecular mechanism of MFG-E8 in ameliorating the rotenone (Rot)-induced L6 skeletal muscle cell oxidative stress injury, differential proteomics of inner L6 cells was conducted. Tandem mass tag (TMT) labeling combined with mass spectrometry (MS) was performed to find associations among control, Rot and Rot + MFG-E8 groups. Over 3248 proteins were identified in the L6 cells. A total of 639 significantly differential proteins were identified, including 294 up-regulated proteins (>1.2 fold) and 345 down-regulated proteins (<0.83 fold) after the exogenous intervention of MFG-E8. Based on the analysis of Gene Ontology (GO), STRING and KEGG databases, MFG-E8 relieves oxidative stress induced-L6 cell damage by regulating the expression of these differential proteins mainly via carbon metabolism, glutathione metabolism and mitochondria-mediated metabolic pathways, e.g. carbohydrate, lipid and amino acid metabolism. Furthermore, to verify the protective effect of MFG-E8 on oxidative stress injured L6 cells, the levels of intracellular reactive oxygen species (ROS), nicotinamide adenine dinucleotide/reduced nicotinamide adenine dinucleotide (NAD⁺/NADH) contents and the protein expression of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) were detected.

Endogenous neural stem cells modulate microglia and protect against demyelination

In response to corpus callosum (CC) demyelination, subventricular zone-derived neural progenitors (SVZdNPs) are mobilized and generate new myelinating oligodendrocytes (OLG). Here, we examine the putative immunomodulatory properties of endogenous SVZdNPs during demyelination in the cuprizone model. SVZdNP density was higher in the lateral and rostral CC regions, and demyelination was inversely correlated with activated microglial density and pro-inflammatory cytokine levels. Single-cell RNA sequencing showed that CC areas with high levels of SVZdNP mobilization were enriched in a microglial cell subpopulation with an immunomodulatory signature. We propose MFGE8 (milk fat globule-epidermal growth factor-8) and β3 integrin as a ligand/receptor pair involved in dialogue between SVZdNPs and microglia. Immature SVZdNPs mobilized to the demyelinated CC were found highly enriched in MFGE8, which promoted the phagocytosis of myelin debris in vitro. Overall, these results demonstrate that, in addition to their cell replacement capacity, endogenous progenitors have immunomodulatory properties, highlighting a new role for endogenous SVZdNPs in myelin regeneration.

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Demyelination is limited in corpus callosum areas rich in subventricular zone–derived progenitors

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In these areas microglial cells adopt an immunomodulatory phenotype

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Mobilized SVZ progenitors secrete MFGE8, which promotes myelin debris phagocytosis

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SVZ-derived progenitors minimize demyelination by modulating microglial activity

The mTOR/NF-κB Pathway Mediates Neuroinflammation and Synaptic Plasticity in Diabetic Encephalopathy

Diabetic encephalopathy, a severe complication of diabetes mellitus, is characterized by neuroinflammation and aberrant synaptogenesis in the hippocampus leading to cognitive decline. Mammalian target of rapamycin (mTOR) is associated with cognition impairment. Nuclear factor-κB (NF-κB) is a transcription factor of proinflammatory cytokines. Although mTOR has been ever implicated in processes occurring in neuroinflammation, the role of this enzyme on NF-κB signaling pathway remains unclear in diabetic encephalopathy. In the present study, we investigated whether mTOR regulates the NF-κB signaling pathway to modulate inflammatory cytokines and synaptic plasticity in hippocampal neurons. In vitro model was constructed in mouse HT-22 hippocampal neuronal cells exposed to high glucose. With the inhibition of mTOR or NF-κB by either chemical inhibitor or short-hairpin RNA (shRNA)-expressing lentivirus-vector, we examined the effects of mTOR/NF-κB signaling on proinflammatory cytokines and synaptic proteins. The diabetic mouse model induced by a high-fat diet combined with streptozotocin injection was administrated with rapamycin (mTOR inhibitor) and PDTC (NF-κB inhibitor), respectively. High glucose significantly increased mTOR phosphorylation in HT-22 cells. While inhibiting mTOR by rapamycin or shmTOR significantly suppressed high glucose-induced activation of NF-κB and its regulators IKKβ and IκBα, suggesting mTOR is the upstream regulator of NF-κB. Furthermore, inhibiting NF-κB by PDTC and shNF-κB decreased proinflammatory cytokines expression (IL-6, IL-1β, and TNF-α) and increased brain-derived neurotrophic factor (BDNF) and synaptic proteins (synaptophysin and PSD-95) in HT-22 cells under high glucose conditions. Besides, the mTOR and NF-κB inhibitors improved cognitive decline in diabetic mice. The inhibition of mTOR and NF-κB suppressed mTOR/NF-κB signaling pathway, increased synaptic proteins, and improved ultrastructural synaptic plasticity in the hippocampus of diabetic mice. Activating mTOR/NF-κB signaling pathway regulates the pathogenesis of diabetic encephalopathy, such as neuroinflammation, synaptic proteins loss, and synaptic ultrastructure impairment. The findings provide the implication that mTOR/NF-κB is potential new drug targets to treat diabetic encephalopathy.

Intranasal insulin improves mitochondrial function and attenuates motor deficits in a rat 6-OHDA model of Parkinson's disease

Aims

Experimental and clinical evidences demonstrate that common dysregulated pathways are involved in Parkinson’s disease (PD) and type 2 diabetes. Recently, insulin treatment through intranasal (IN) approach has gained attention in PD, although the underlying mechanism of its potential therapeutic effects is still unclear. In this study, we investigated the effects of insulin treatment in a rat model of PD with emphasis on mitochondrial function indices in striatum.

Methods

Rats were treated with a daily low dose (4IU/day) of IN insulin, starting 72 h after 6‐OHDA‐induced lesion and continued for 14 days. Motor performance, dopaminergic cell survival, mitochondrial dehydrogenases activity, mitochondrial swelling, mitochondria permeability transition pore (mPTP), mitochondrial membrane potential (Δψ_m), reactive oxygen species (ROS) formation, and glutathione (GSH) content in mitochondria, mitochondrial adenosine triphosphate (ATP), and the gene expression of PGC‐1α, TFAM, Drp‐1, GFAP, and Iba‐1 were assessed.

Results

Intranasal insulin significantly reduces 6‐OHDA‐induced motor dysfunction and dopaminergic cell death. In parallel, it improves mitochondrial function indices and modulates mitochondria biogenesis and fission as well as activation of astrocytes and microglia.

Conclusion

Considering the prominent role of mitochondrial dysfunction in PD pathology, IN insulin as a disease‐modifying therapy for PD should be considered for extensive research.

Propofol suppresses microglial phagocytosis through the downregulation of MFG-E8

BACKGROUND

Microglia are highly motile phagocytic cells in the healthy brain with surveillance and clearance functions. Although microglia have been shown to engulf cellular debris following brain insult, less is known about their phagocytic function in the absence of injury. Propofol can inhibit microglial activity, including phagocytosis. Milk fat globule epidermal growth factor 8 (MFG-E8), as a regulator of microglia, plays an essential role in the phagocytic process. However, whether MFG-E8 affects the alteration of phagocytosis by propofol remains unknown.

METHODS

Microglial BV2 cells were treated with propofol, with or without MFG-E8. Phagocytosis of latex beads was evaluated by flow cytometry and immunofluorescence. MFG-E8, p-AMPK, AMPK, p-Src, and Src levels were assessed by western blot analysis. Compound C (AMPK inhibitor) and dasatinib (Src inhibitor) were applied to determine the roles of AMPK and Src in microglial phagocytosis under propofol treatment.

RESULTS

The phagocytic ability of microglia was significantly decreased after propofol treatment for 4 h (P < 0.05). MFG-E8 production was inhibited by propofol in a concentration- and time-dependent manner (P < 0.05). Preadministration of MFG-E8 dose-dependently (from 10 to 100 ng/ml) reversed the suppression of phagocytosis by propofol (P < 0.05). Furthermore, the decline in p-AMPK and p-Src levels induced by propofol intervention was reversed by MFG-E8 activation (P < 0.05). Administration of compound C (AMPK inhibitor) and dasatinib (Src inhibitor) to microglia blocked the trend of enhanced phagocytosis induced by MFG-E8 (P < 0.05).

CONCLUSIONS

These findings reveal the intermediate role of MFG-E8 between propofol and microglial phagocytic activity. Moreover, MFG-E8 may reverse the suppression of phagocytosis induced by propofol through the regulation of the AMPK and Src signaling pathways.

MFG-E8 attenuates inflammation in subarachnoid hemorrhage by driving microglial M2 polarization

Increasing evidence suggests that microglial polarization plays an important role in the pathological processes of neuroinflammation following subarachnoid hemorrhage (SAH). Previous studies indicated that milk fat globule-epidermal growth factor-8 (MFG-E8) has potential anti-apoptotic and anti-inflammatory effects in cerebral ischemia. However, the effects of MFG-E8 on microglial polarization have not been evaluated after SAH. Therefore, the aim of this study was to explore the role of MFG-E8 in anti-inflammation, and its effects on microglial polarization following SAH. We established the SAH model via prechiasmatic cistern blood injection in mice. Double-immunofluorescence staining, western blotting and quantitative real-time polymerase chain reaction (q-PCR) were performed to investigate the expression and cellular distribution of MFG-E8. Two different dosages (1 and 5 μg) of recombinant human MFG-E8 (rhMFG-E8) were injected intracerebroventricularly (i.c.v.) at 1 h after SAH. Brain water content, neurological scores, beam-walking score, Fluoro-Jade C (FJC), and terminal deoxynucleotidyl transferase dUTP nick endlabeling staining (TUNEL) were measured at 24 h. Suppression of MFG-E8, integrin β3 and phosphorylation of STAT3 were achieved by specific siRNAs (500 pmol/5 μl) and the STAT3 inhibitor Stattic (5 μM). The potential signaling pathways and microglial polarization were measured by immunofluorescence labeling and western blotting. SAH induction increased the levels of inflammatory mediators and the proportion of M1 cells, and caused neuronal apoptosis in mice at 24 h. Treatment with rhMFG-E8 (5 μg) remarkably decreased brain edema, improved neurological functions, reduced the levels of proinflammatory factors, and promoted the microglial to shift to M2 phenotype. However, knockdown of MFG-E8 and integrin β3 via siRNA abolished the effects of MFG-E8 on anti-inflammation and M2 phenotype polarization. The STAT3 inhibitor Stattic further clarified the role of rhMFG-E8 in microglial polarization by regulating the protein levels of the integrin β3/SOCS3/STAT3 pathway. rhMFG-E8 inhibits neuronal inflammation by transformation the microglial phenotype toward M2 and its direct protective effect on neurons after SAH, which may be mediated by modulation of the integrin β3/SOCS3/STAT3 signaling pathway, highlighting rhMFG-E8 as a potential therapeutic target for the treatment of SAH patients.

Inflammatory factors and amyloid β-induced microglial polarization promote inflammatory crosstalk with astrocytes

The immunological responses are a key pathological factor in Alzheimer's disease (AD). We hypothesized that microglial polarization alters microglia-astrocyte immune interactions in AD. M1 and M2 microglia were isolated from primary rat microglia and were confirmed to secrete pro-inflammatory and anti-inflammatory factors, respectively. Primary rat astrocytes were co-cultured with M1 or M2 microglial medium. M1 microglial medium increased astrocyte production of pro-inflammatory factors (interleukin [IL]-1β, tumor necrosis factor α and IL-6), while M2 microglial medium enhanced astrocyte production of anti-inflammatory factors (IL-4 and IL-10). To analyze the crosstalk between microglia and astrocytes after microglial polarization specifically in AD, we co-cultured astrocytes with medium from microglia treated with amyloid-β (Aβ) alone or in combination with other inflammatory substances. Aβ alone and Aβ combined with lipopolysaccharide/interferon-γ induced pro-inflammatory activity in M1 microglia and astrocytes, whereas IL-4/IL-13 inhibited Aβ-induced pro-inflammatory activity. Nuclear factor κB p65 was upregulated in M1 microglia and pro-inflammatory astrocytes, while Stat6 was upregulated in M2 microglia and anti-inflammatory astrocytes. These results provide direct evidence that microglial polarization governs communication between microglia and astrocytes, and that AD debris alters this crosstalk.

A novel polysaccharide from Acorus tatarinowii protects against LPS-induced neuroinflammation and neurotoxicity by inhibiting TLR4-mediated MyD88/NF-κB and PI3K/Akt signaling pathways

Our previous study has indicated that a crude polysaccharide derived from Acorus tatarinowii, AT50, remarkably improves learning and memory in scopolamine-induced amnesic mice and prevents the release of inflammatory mediators. To further explore the bioactive constituents of AT50, a novel polysaccharide (ATP50-3) was purified, and its anti-neuroinflammatory effects and underlying mechanisms were investigated. ATP50-3 significantly reduced abnormal elevation of inflammatory mediators in lipopolysaccharide (LPS)-induced proinflammatory BV2 cells in vitro and inhibited the activation of nuclear factor kappa B (NF-κB). Moreover, ATP50-3 down-regulated LPS-induced protein levels of Toll-like receptor 4 (TLR4), myeloid differentiation primary response protein (MyD88), p-PI3K (phosphoinositide 3-kinase), and p-Akt (protein kinase B). Further experiments demonstrated that TAK242 (a TLR4 inhibitor) and LY294002 (a PI3K inhibitor) remarkably augmented ATP50-3's down-regulation on LPS-induced proinflammatory mediators. Importantly, ATP50-3 provided neuroprotection against neuroinflammation-induced neurotoxicity in primary cortical and hippocampal neurons by mitigating overproduction of reactive oxygen species and damage to the mitochondrial membrane potential (MMP). Taken together, our findings suggest that ATP50-3 exerts anti-neuroinflammatory and neuroprotective effects through modulation of TLR4-mediated MyD88/NF-κB and PI3K/Akt signaling pathways.

Using the Metabolome to Understand the Mechanisms Linking Chronic Arsenic Exposure to Microglia Activation, and Learning and Memory Impairment

The activation of microglia is a hallmark of neuroinflammation and contributes to various neurodegenerative diseases. Chronic inorganic arsenic exposure is associated with impaired cognitive ability and increased risk of neurodegeneration. The present study aimed to investigate whether chronic inorganic arsenic-induced learning and memory impairment was associated with microglial activation, and how organic (DMA^V 600 μM, MMA^V 0.1 μM) and inorganic arsenic (NaAsO2 0.6 μM) affect the microglia. Male C57BL/6J mice were divided into two groups: a control group and a group exposed to arsenic in their drinking water (50 mg/L NaAsO2 for 24 weeks). The Morris water maze was performed to analyze neuro-behavior and transmission electron microscopy was used to assess alterations in cellular ultra-structures. Hematoxylin-eosin and Nissl staining were used to observe pathological changes in the cerebral cortex and hippocampus. Flow cytometry was used to reveal the polarization of the arsenic-treated microglia phenotype and GC-MS was used to assess metabolomic differences in the in vitro microglia BV-2 cell line model derived from mice. The results showed learning and memory impairments and activation of microglia in the cerebral cortex and dentate gyrus (DG) zone of the hippocampus, in mice chronically exposed to arsenic. Flow cytometry demonstrated that BV-2 cells were activated with the treatment of different arsenic species. The GC-MS data showed three important metabolites to be at different levels according to the different arsenic species used to treat the microglia. These included tyrosine, arachidonic acid, and citric acid. Metabolite pathway analysis showed that a metabolic pathways associated with tyrosine metabolism, the dopaminergic synapse, Parkinson's disease, and the citrate cycle were differentially affected when comparing exposure to organic arsenic and inorganic arsenic. Organic arsenic MMA^V was predominantly pro-inflammatory, and inorganic arsenic exposure contributed to energy metabolism disruptions in BV-2 microglia. Our findings provide novel insight into understanding the neurotoxicity mechanisms of chronic arsenic exposure and reveal the changes of the metabolome in response to exposure to different arsenic species in the microglia.

Microglia induce the transformation of A1/A2 reactive astrocytes via the CXCR7/PI3K/Akt pathway in chronic post-surgical pain

Background

Activated astrocytes play important roles in chronic post-surgical pain (CPSP). Recent studies have shown reactive astrocytes are classified into A1 and A2 phenotypes, but their precise roles in CPSP remain unknown. In this study, we investigated the roles of spinal cord A1 and A2 astrocytes and related mechanisms in CPSP.

Methods

We used a skin/muscle incision and retraction (SMIR) model to establish a rat CPSP model. Microglia, CXCR7, and the phosphoinositide 3-kinase/Akt (PI3K/Akt) signaling pathways were regulated by intrathecal injections of minocycline (a non-specific microglial inhibitor), AMD3100 (a CXCR7 agonist), and LY294002 (a specific PI3K inhibitor), respectively. Mechanical allodynia was detected with von Frey filaments. The changes in microglia, A1 astrocytes, A2 astrocytes, CXCR7, and PI3K/Akt signaling pathways were examined by enzyme-linked immunosorbent assay (ELISA), western blot, and immunofluorescence.

Results

Microglia were found to be activated, with an increase in interleukin-1 alpha (IL-1α), tumor necrosis factor alpha (TNFα), and complement component 1q (C1q) in the spinal cord at an early stage after SMIR. On day 14 after SMIR, spinal cord astrocytes were also activated; these were mainly of the A1 phenotype and less of the A2 phenotype. Intrathecal injection of minocycline relieved SMIR-induced mechanical allodynia and reverted the ratio of A1/A2 reactive astrocytes. The expression of CXCR7 and PI3K/Akt signaling was decreased after SMIR, while they were increased after treatment with minocycline. Furthermore, intrathecal injection of AMD3100 also relieved SMIR-induced mechanical allodynia, reverted the ratio of A1/A2 reactive astrocytes, and activated the PI3K/Akt signaling pathway, similar to the effects produced by minocycline. However, intrathecal injection of AMD3100 did not increase the analgesic effect of minocycline. Last, LY294002 inhibited the analgesic effect and A1/A2 transformation induced by minocycline and AMD3100 after SMIR.

Conclusion

Our results indicated that microglia induce the transformation of astrocytes to the A1 phenotype in the spinal cord via downregulation of the CXCR7/PI3K/Akt signaling pathway during CPSP. Reverting A1 reactive astrocytes to A2 may represent a new strategy for preventing CPSP.

Synaptic Pruning in Alzheimer's Disease: Role of the Complement System

Alz heimer’s disease (AD) continues to threaten aged individuals and health care systems around the world. Human beings have been trying to postpone, reduce, or eliminate the primary risk factor for AD, aging, throughout history. Despite this, there is currently only symptomatic treatment for AD and this treatment is limited to only a handful of FDA approved AD drugs.

Neuroimmunomodulatory and Neuroprotective Effects of the Flavonoid Apigenin in in vitro Models of Neuroinflammation Associated With Alzheimer's Disease

Neurodegenerative disorders (ND) are characterized by the progressive and irreversible loss of neurons. Alzheimer’s Disease (AD) is the most incident age-related ND, in which the presence of a chronic inflammatory compound seems to be related to its pathogenesis. Different stimuli in the central nervous system (CNS) can induce activation, proliferation, and changes in phenotype and glial function, which can be modulated by anti-inflammatory agents. Apigenin (4,5,7–trihydroxyflavone) is a flavonoid found in abundance in many fruits and vegetables, that has shown important effects upon controlling the inflammatory response. This study evaluated the neuroprotective and neuroimmunomodulatory potential of apigenin using in vitro models of neuroinflammation associated with AD. Co-cultures of neurons and glial cells were obtained from the cortex of newborn and embryonic Wistar rats. After 26 days in vitro, cultures were exposed to lipopolysaccharide (LPS; 1 μg/ml), or IL-1β (10 ng/ml) for 24 h, or to Aβ oligomers (500 nM) for 4 h, and then treated with apigenin (1 μM) for further 24 h. It was observed that the treatment with apigenin preserved neurons and astrocytes integrity, determined by Rosenfeld’s staining and immunocytochemistry for β-tubulin III and GFAP, respectively. Moreover, it was observed by Fluoro-Jade-B and caspase-3 immunostaining that apigenin was not neurotoxic and has a neuroprotective effect against inflammatory damage. Additionally, apigenin reduced microglial activation, characterized by inhibition of proliferation (BrdU+ cells) and modulation of microglia morphology (Iba-1 + cells), and decreased the expression of the M1 inflammatory marker CD68. Moreover, as determined by RT-qPCR, inflammatory stimuli induced by IL-1β increased the mRNA expression of IL-6, IL-1β, and CCL5, and decreased the mRNA expression of IL-10. Contrary, after treatment with apigenin in inflammatory stimuli (IL-1β or LPS) there was a modulation of the mRNA expression of inflammatory cytokines, and reduced expression of OX42, IL-6 and gp130. Moreover, apigenin alone and after an inflammatory stimulus with IL-1β also induced the increase in the expression of brain-derived neurotrophic factor (BDNF), an effect that may be associated with anti-inflammatory and neuroprotective effects. Together these data demonstrate that apigenin presents neuroprotective and anti-inflammatory effects in vitro and might represent an important neuroimmunomodulatory agent for the treatment of neurodegenerative conditions.

Cerebrospinal fluid MFG-E8 as a promising biomarker of amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a fatal progressive neurodegenerative disease resulting in the dysfunction of upper and lower motor neurons. Biomarkers in fluid have been used to monitor the disease and its progression. Milk fat globule-EGF factor 8 (MFG-E8) is an inflammation modulator, which is involved in the pathogenesis of neurodegenerative diseases. We here took this study to evaluate the predictive value of MFG-E8 in ALS.

METHODS

This study consisted of 19 patients with ALS and 15 healthy controls. Cerebrospinal fluid (CSF) were collected from all participants and tested for the levels of MFG-E8, neurofilament light (NFL), and heavy chain (NFH). The correlations between MFG-E8 and NFL, NFH, ALS severity, cognitive status, and forced vital capacity (FVC) were analyzed.

RESULTS

We found that MFG-E8 performs well in distinguishing ALS from controls, with relatively higher level of MFG-E8 in ALS subjects, than controls. Moreover, MFG-E8 negatively correlated with the revised ALS function rating scale (ALS-FRS), but not with the levels of NFL and NFH, disease duration, progression rate, mini-mental state examination (MMSE), and FVC.

CONCLUSIONS

The study proved that CSF MFG-E8 helps distinguish ALS from controls. However, the protein in CSF negatively predicted disease severity.

Dynorphin activation of kappa opioid receptor promotes microglial polarization toward M2 phenotype via TLR4/NF-κB pathway

Background

Microglia-mediated neuroinflammation is associated with epilepsy. Switching microglial polarization from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype represents a novel therapeutic strategy for mitigating epileptogenesis. We previously found that dynorphins protected against epilepsy via activation of kappa opioid receptor (KOR). Here, this study aims to investigate the role and the mechanism of dynorphin in regulating microglial polarization.

Methods

A pilocarpine-induced rat model of epilepsy was established and lipopolysaccharide (LPS)-activated BV-2 microglial cells were used as an inflammatory model to explore the mechanism of dynorphin regulating microglial polarization.

Results

Overexpression of the dynorphin precursor protein prodynorphin (PDYN) alleviated the pilocarpine-induced neuronal apoptosis, promoted microglial polarization to the M2 phenotype, and inhibited pilocarpine-induced Toll-like receptor 4 (TLR4)/nuclear factor-kappa B (NF-κB) pathway in the hippocampi of epileptic rats. Dynorphin activation of KOR promoted microglial M2 polarization via inhibiting TLR4/NF-κB pathway in LPS-stimulated BV-2 microglial cells. Moreover, dynorphin/KOR regulated microglial M2 polarization inhibited apoptosis of the primary mouse hippocampal neurons.

Conclusion

In conclusion, dynorphin activation of KOR promotes microglia polarization toward M2 phenotype via inhibiting TLR4/NF-κB pathway.

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.

Milk Fat Globule-Epidermal Growth Factor-Factor 8 Reverses Lipopolysaccharide-Induced Microglial Oxidative Stress

Oxidative stress plays an important role in various neurological disorders. Milk fat globule-epidermal growth factor-factor 8 (MFG-E8) is a regulatory protein for microglia. However, its involvement in microglial oxidative stress has not been established. In this study, we observed microglial oxidative stress in response to lipopolysaccharide (LPS) both in vitro and in vivo. LPS induced significant elevation of TNF-α, IL-6, MDA, and ROS and reduction of GSH and SOD in the mouse brains and primary microglia, which were reversed by MFG-E8 pretreatment. MFG-E8 induced the expression of Nrf-2 and HO-1 that was reduced by LPS incubation. Moreover, LPS-increased Keap-1 expression was reversed by MFG-E8. But the above tendencies were not seen when MFG-E8 was applied alone. The current study established the involvement of MFG-E8 in antioxidant effects during neuroinflammation. It may achieve the effects through the regulation of Keap-1/Nrf-2/HO-1 pathways.

2D:4D Ratio Differs in Ischemic Stroke: A Single Center Experience

Background

The index to ring finger length (2D:4D) ratio is a proxy biomarker for prenatal exposure of sex hormones. Sex hormones are associated with the pathogenesis of ischemic stroke. The purpose of the study was to demonstrate the association between 2D:4D and ischemic stroke.

Methodology

This study retrospectively reviewed the data of 100 patients with first ever ischemic stroke between September, 2016 and June, 2017. The lengths of index finger and ring finger of both hands were measured using electronic calipers and calculated for 2D:4D ratios. Receive operating characteristic (ROC) mode was used to detect predicting performance of 2D:4D ratios for ischemic stroke.

Results

2D:4D ratios in ischemic stroke patients were higher than controls in both hands (P < 0.05), except right 2D:4D ratio in females. The ROC analyses showed that the area under the curve (AUC) were 0.635 (95%CI: 0.527-0.743) for left 2D:4D ratio, and 0.647 for right (95%CI: 0.539-0.755) (P < 0.05). The AUC of left and right 2D:4D ratio in male were 0.667 (95%CI: 0.514-0.820) and 0.670 (95%CI: 0.519-0.822) (P < 0.05). In female, no significance were found in ROC analysis. And there were no correlation between 2D:4D value and stroke severity (P > 0.05).

Conclusions

The current study indicated that the diagnostic value of 2D:4D ratio was limited in ischemic stroke. Further research is required to explore the role of it in screening ischemic stroke.

BACE1 gene silencing alleviates isoflurane anesthesia‑induced postoperative cognitive dysfunction in immature rats by activating the PI3K/Akt signaling pathway

Postoperative cognitive dysfunction (POCD) is a severe complication characterized by cognitive dysfunction following anesthesia and surgery. The aim of the present study was to investigate the effects of β-site amyloid precursor protein cleavage enzyme 1 (BACE1) gene silencing on isoflurane anesthesia-induced POCD in immature rats via the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt) signaling pathway. Rat models were established and then transfected with BACE1 small interfering RNA and wortmannin (an inhibitor of PI3K). Blood gas analysis was performed, and a series of behavioral experiments were conducted to evaluate the cognitive function, learning ability and locomotor activity of rats. Reverse transcription quantitative polymerase chain reaction and western blot analysis were employed to determine the mRNA and protein expression of the associated genes. An ELISA was used to detect the inflammatory indicators and the content of amyloid precursor protein (APP) and amyloid-β (Aβ). Apoptosis of the hippocampal CA1 region was observed by terminal deoxynucleotidyl transferase dUTP nick-end labeling staining. Initially, it was revealed that the percentage of stagnation time in rats was increased by BACE1 gene silencing; the escape latency and swimming distance were markedly reduced from the 4th to the 6th day, the time the rats spent in first passing the target area was shortened, and the times of passing the target area were increased by BACE1 gene silencing, demonstrating that BACE1 gene silencing enhanced the spatial memory ability of rats. Additionally, it was determined that silencing BACE1 improved the pathological state induced by isoflurane anesthesia in immature rats, and attenuated the inflammatory response and the levels of APP and Aβ in hippocampal tissues. Furthermore, it was suggested that silencing BACE1 may have promoted the activation of the PI3K/Akt signaling pathway, thereby inhibiting the apoptosis of the hippocampal CA1 region. Taken together, these results indicated that BACE1 gene silencing may improve isoflurane anesthesia-induced POCD in immature rats by activating the PI3K/Akt signaling pathway and inhibiting the Aβ generated by APP.

Recombinant milk fat globule-EGF factor-8 reduces apoptosis via integrin β3/FAK/PI3K/AKT signaling pathway in rats after traumatic brain injury

Accumulating evidence suggests neuronal apoptosis has the potential to lead to more harmful effects in the pathological processes following traumatic brain injury (TBI). Previous studies have established that milk fat globule-EGF factor-8 (MFG-E8) provides neuroprotection through modulation of inflammation, oxidative stress, and especially apoptosis in cerebral ischemia and neurodegenerative disease. However, the effects of MFG-E8 on neuronal apoptosis in TBI have not yet been investigated. Therefore, we explored the role of MFG-E8 on anti-apoptosis and its potential mechanism following TBI. In the first set of experiments, adult male Sprague–Dawley (SD) rats were randomly divided into Sham and TBI groups that were each further divided into five groups representing different time points (6 h, 24 h, 72 h, and 7 days) (n = 9 each). Western blotting, quantitative real-time PCR, and immunofluorescence staining were performed to identify the expression and cellular localization of MFG-E8. In the second set of experiments, four groups were randomly assigned: Sham group, TBI + Vehicle group, and TBI + rhMFG-E8 (1 and 3 µg) (n = 15). Recombinant human MFGE8 (rhMFG-E8) was administrated as two concentrations through intracerebroventricular (i.c.v.) injection at 1 h after TBI induction. Brain water content, neurological severity score, western blotting, and immunofluorescence staining were measured at 24 and 72 h following TBI. In the final set of experiments, MFG-E8 siRNA (500 pmol/3 µl), integrin β3 siRNA (500 pmol/3 µl), and PI3K inhibitor LY294002 (5 and 20 µM) were injected i.c.v. and thereafter rats exposed to TBI. Western blotting, immunofluorescence staining, brain water content, neurological severity score, and Fluoro-Jade C (FJC) staining were used to investigate the effect of the integrin-β3/FAK/PI3K/AKT signaling pathway on MFG-E8-mediated anti-apoptosis after TBI. The expression of MFG-E8 was mainly located in microglial cells and increased to peak at 24 h after TBI. Treatment with rhMFG-E8 (3 µg) markedly decreased brain water content, improved neurological deficits, and reduced neuronal apoptosis at 24 and 72 h after TBI. rhMFG-E8 significantly enhanced the expression of integrin-β3/FAK/PI3K/AKT pathway-related components. Administration of integrin-β3 siRNA and LY294002 (5 and 20 µM) abolished the effect of rhMFG-E8 on anti-apoptosis and neuroprotection after TBI. This study demonstrated for the first time that rhMFG-E8 inhibits neuronal apoptosis and offers neuroprotection. This is suggested to occur through the modulation of the integrin-β3/FAK/PI3K/AKT signaling pathway, highlighting rhMFG-E8 as a potentially promising therapeutic strategy for TBI patients.

MFG-E8 reverses microglial-induced neurotoxic astrocyte (A1) via NF-κB and PI3K-Akt pathways

Recent evidence have suggested that neuroinflammation and ischemia induce the activation of two different types of reactive astrocytes, termed A1 and A2. Additionally, A1 astrocytes contribute to the death of neurons and oligodendrocytes in neurodegenerative diseases, such as Alzheimer's disease (AD). In the current study, we constructed an Aβ42-activated microglia-conditioned medium to induce A1 astrocytic activation via secretion of interleukin 1α, tumor necrosis factor, and complement component 1q in vitro, and indicated the regulatory role of milk fat globule epidermal growth factor 8 (MFG-E8) on A1/A2 astrocytic alteration through the downregulation of nuclear factor-κB and the upregulation of PI3K-Akt. This study showed that MFG-E8 suppressed A1 astrocytes and holds great potential for the treatment of AD.

Paeoniflorin exerts neuroprotective effects by modulating the M1/M2 subset polarization of microglia/macrophages in the hippocampal CA1 region of vascular dementia rats via cannabinoid receptor 2

Background

Cerebral hypoperfusion is a pivotal risk factor for vascular dementia (VD), for which effective therapy remains inadequate. Persistent inflammatory responses and excessive chemotaxis of microglia/macrophages in the brain may accelerate the progression of VD. Endocannabinoids are involved in neuronal protection against inflammation-induced neuronal injury. Cannabinoids acting at cannabinoid receptor 2 (CB₂R) can decrease inflammation. Based on the identification of paeoniflorin (PF) as a CB₂R agonist, we investigated the neuroprotective and microglia/macrophages M1 to M2 polarization promoting effects of PF in a permanent four-vessel occlusion rat model.

Methods

One week after surgery, PF was intraperitoneally administered at a dose of 40 mg/kg once a day for 28 successive days. The effects of PF on memory deficit were investigated by a Morris water maze test, and the effects of PF on hippocampal neuronal damage were evaluated by light microscope and electron microscope. The mRNA and protein expression levels of key molecules related to the M1/M2 polarization of microglia/macrophages were assessed by RT-qPCR and Western blotting, respectively.

Results

Administration of PF could significantly attenuate cerebral hypoperfusion-induced impairment of learning and memory and reduce the morphological and ultrastructural changes in the hippocampal CA1 region of rats. Moreover, PF promoted an M1 to M2 phenotype transition in microglia/macrophages in the hippocampus of rats. In addition to its inhibitory property against proinflammatory M1 mediator expression, such as IL-1β, IL-6, TNF-α and NO, PF dramatically up-regulated expression of anti-inflammatory cytokines IL-10 and TGF-β1. Importantly, CB₂R antagonist AM630 abolished these beneficial effects produced by PF on learning, memory and hippocampus structure in rats, as well as the polarization of microglia/macrophages to the M2 phenotype. Additionally, PF treatment significantly inhibited cerebral hypoperfusion-induced mTOR/NF-κB proinflammatory pathway and enhanced PI3K/Akt anti-inflammatory pathway. Effects of PF on these signaling pathways were effectively attenuated when rats were co-treated with PF and AM630, indicating that the mTOR/NF-κB and PI3K/Akt signaling pathways were involved in the PF effects through CB₂R activation.

Conclusion

These findings demonstrated PF exerts its neuroprotective effect and shifts the inflammatory milieu toward resolution by modulation of microglia/macrophage polarization via CB₂R activation.

Electronic supplementary material

The online version of this article (10.1186/s13020-018-0173-1) contains supplementary material, which is available to authorized users.