Paraquat modulates microglia M1/M2 polarization via activation of TLR4-mediated NF-κB signaling pathway

Discovery and verification of antidepressant active ingredients of raw and vinegar-processed Bupleurum marginatum var. Stenophyllum based on plant metabolomics and serum pharmacology

The dried root of Bupleurum marginatum var. stenophyllum (H. Wolff) R.H. Shan & Y. Li (BM), which has been used as a Bupleuri radix in Guizhou Province and is listed in the 2003 edition of the Guizhou Quality Standard for Traditional Chinese Medicines and Ethnic Materia Medica, is effective at dispersing the liver and relieving depression and often used in the form of raw or vinegar-processed product (VBM). However, the potential depression-relieving components of BM are unclear. The aim of this study was to determine the potential antidepressant constituents of BM and investigate the effect of vinegar processing on these components. The antidepressant effect and mechanism of BM and VBM were investigated in depressed mice and BV2 cells, respectively. The pharmacodynamic constituents were screened through serum pharmacochemistry, which combined the results of metabolomics analysis of BM and VBM, high-performance liquid chromatography (HPLC) content determination, and verification of the antidepressant effect and mechanism of differential components of SSb2 to clarify the connotation of vinegar processing. Our results demonstrated that BM can exert a significant antidepressant effect by inhibiting microglia polarization and that this effect was enhanced after vinegar processing. Thirty-eight components were identified in the BM, 13 of which were blood-absorbable, mainly saponins, and defined as potential antidepressant components of the BM. The contents of 17 components-6 of which were absorbed into the blood-changed considerably after processing. It was finally determined that vinegar processing can enhance the antidepressant effect of BM by increasing the contents of SSb1 and SSb2. SSb2 exerts this effect via the samemechanism as BM. In conclusion, in this study we clarified the antidepressant effects and potential active components of BM and examined the mechanism of vinegar processing. These findings lay a foundation for the future research on the antidepressant effects of BM as well as for the complete development and application of BM's ethnomedicinal resources.

An approach based on a combination of toxicological experiments and in silico predictions to investigate the adverse outcome pathway (AOP) of paraquat neuro-immunotoxicity

Paraquat (PQ) exposure is strongly associated with neurotoxicity. However, research on the neurotoxicity mechanisms of PQ varies in terms of endpoints of toxic assessment, resulting in a great challenge to understand the early neurotoxic effects of PQ. In this study, we developed an adverse outcome pathway (AOP) to investigate PQ-induced neuro-immunotoxicity from an immunological perspective, combining of traditional toxicology methods and computer simulations. In vivo, PQ can microstructurally lead to an early synaptic loss in the brain mice, which is a large degree regarded as a main reason for cognitive impairment to mice behavior. Both in vitro and in vivo demonstrated synapse loss is caused by excessive activation of the complement C1q/C3-CD11b pathway, which mediates microglial phagocytosis dysfunction. Additionally, the interaction between PQ and C1q was validated by molecular simulation docking. Our findings extend the AOP framework related to PQ neurotoxicity from a neuro-immunotoxic perspective, highlighting C1q activation as the initiating event for PQ-induced neuro-immunotoxicity. In addition, downstream complement cascades induce abnormal microglial phagocytosis, resulting in reduced synaptic density and subsequent non-motor dysfunction. These findings deepen our understanding of neurotoxicity and provide a theoretical basis for ecological risk assessment of PQ.

Inhibition of the TLR4/NF-κB pathway promotes the polarization of LPS-induced BV2 microglia toward the M2 phenotype

This study aimed to investigate whether the inhibition of the TLR4/NF-κB pathway can promote lipopolysaccharide (LPS)-induced microglial polarization from the M1 to M2 phenotype, and thus exert neuroprotection. LPS-induced microglia were used as a model for inflammation in vitro. TLR4-specific inhibitor resatorvid (TAK-242) and NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC) were used to verify the effect of the TLR4/NF-κB pathway on microglia activation and polarization. Cell proliferation was measured by cell counting, and nitric oxide (NO) and reactive oxygen species (ROS) release was measured using the Griess reagent and ROS kit, respectively. Immunofluorescence and RT-qPCR analyses were used to detect the expression of microglial activation markers, phenotypic markers, related pathway molecules, and inflammatory factors. TLR4 specific inhibitor TAK-242 and NF-κB inhibitor PDTC alleviated LPS-induced microglia over-activation by inhibiting the TLR4/NF-κB pathway, and reduced LPS-stimulated cell proliferation and the release of NO, ROS, TNF-a, and IL-6 and IL-1β. Meanwhile, TAK-242 and PDTC promoted LPS-induced polarization of microglia from M1 to M2 phenotype, decreased the expression of microglial activation marker Iba1 and M1 phenotypic markers (TNF-a and CD86), and increased the expression of M2 phenotypic markers (Arg-1 and CD206). The mechanism may be related to inhibiting the TLR4/NF-κB pathway. The inhibition of the TLR4/NF-κB pathway can promote LPS-induced polarization of BV2 microglia from M1 phenotype to M2 phenotype.

CXCR4-BTK axis mediate pyroptosis and lipid peroxidation in early brain injury after subarachnoid hemorrhage via NLRP3 inflammasome and NF-κB pathway

C-X-C chemokine receptor type 4 (CXCR4) is critical for homeostasis of the adaptive and innate immune system in some CNS diseases. Bruton's tyrosine kinase (BTK) is an essential kinase that regulates inflammation in immune cells through multiple signaling pathways. This study aims to explore the effect of CXCR4 and BTK on neuroinflammation in the pathogenesis of early brain injury (EBI) after subarachnoid hemorrhage (SAH). Our results showed that the expression of CXCR4 and p-BTK increased significantly at 24 h after SAH in vivo and in vitro. Ibrutinib improved neurological impairment, BBB disruption, cerebral edema, lipid peroxidation, neuroinflammation and neuronal death at 24 h after SAH. Inhibition of BTK phosphorylation promoted the in vitro transition of hemin-treated proinflammatory microglia to the anti-inflammatory state, inhibited the p-P65 expression and microglial pyroptosis. NLRP3 deficiency can significantly reduce pyroptosis in SAH mice. Moreover, CXCR4 inhibition can suppress NLRP3-mediated pyroptosis, NF-κB activation and NOX2 expression in vitro, and ibrutinib can abolish CXCR4-aggravated BBB damage and pyroptosis in EBI after SAH. The levels of CXCR4 in CSF of SAH patients is significantly increased, and it is positively correlated with GSDMD and IL-1β levels, and have a moderate diagnostic value for outcome at 6-month follow-up. Our findings revealed the effect of CXCR4 and P-BTK on NLRP3-mediated pyroptosis and lipid peroxidation after SAH in vivo and in vitro, and the potential diagnostic role of CXCR4 in CSF of SAH patients. Inhibition of CXCR4-BTK axis can significantly attenuate NLRP3-mediated pyroptosis and lipid peroxidation by regulating NF-κB activation in EBI after SAH.

Rice Germ Ameliorated Chronic Unpredictable Mild Stress-Induced Depressive-like Behavior by Reducing Neuroinflammation

Stress-induced neuroinflammation is widely regarded as one of the primary causes of depression. Gamma-aminobutyric acid (GABA)-enriched foods relieve stress and reduce inflammatory reactions. This study aimed to evaluate whether rice germ with 30% GABA (RG) reduced neuroinflammation in mice exposed to chronic unpredictable mild stress (CUMS). CUMS mice were administered 40, 90, and 140 mg/kg of RG. CUMS increased serum and hypothalamic pro-inflammatory cytokine (TNF-α and IL-6) levels, which were decreased by RG. In the hypothalamus, CUMS elevated M1-type microglia markers of CD86 and NF-κB, whereas RG lowered these levels. The expression levels of NLRP3 inflammasome complex (NLRP3, apoptosis-associated speck-like protein containing a caspase recruitment domain, and caspase-1), IL-1β, and IL-18 were increased in the hypothalamus of CUMS mice and decreased by RG. RG attenuated depressive-like behaviors in CUMS mice, as measured by the forced swim test and tail suspension test. In conclusion, RG decreased hypothalamic inflammation-related signals, such as TNF-α, IL-6, M1 polarization, NF-κB, NLRP3 inflammasome complex, caspase-1, IL-1β, and IL-18, to diminish depressive-like behavior.

Modulation of the Microglial Nogo-A/NgR Signaling Pathway as a Therapeutic Target for Multiple Sclerosis

Current therapeutics targeting chronic phases of multiple sclerosis (MS) are considerably limited in reversing the neural damage resulting from repeated inflammation and demyelination insults in the multi-focal lesions. This inflammation is propagated by the activation of microglia, the endogenous immune cell aiding in the central nervous system homeostasis. Activated microglia may transition into polarized phenotypes; namely, the classically activated proinflammatory phenotype (previously categorized as M1) and the alternatively activated anti-inflammatory phenotype (previously, M2). These transitional microglial phenotypes are dynamic states, existing as a continuum. Shifting microglial polarization to an anti-inflammatory status may be a potential therapeutic strategy that can be harnessed to limit neuroinflammation and further neurodegeneration in MS. Our research has observed that the obstruction of signaling by inhibitory myelin proteins such as myelin-associated inhibitory factor, Nogo-A, with its receptor (NgR), can regulate microglial cell function and activity in pre-clinical animal studies. Our review explores the microglial role and polarization in MS pathology. Additionally, the potential therapeutics of targeting Nogo-A/NgR cellular mechanisms on microglia migration, polarization and phagocytosis for neurorepair in MS and other demyelination diseases will be discussed.

Glial cell reactivity and oxidative stress prevention in Alzheimer's disease mice model by an optimized NMDA receptor antagonist

In Alzheimer's disease pathology, several neuronal processes are dysregulated by excitotoxicity including neuroinflammation and oxidative stress (OS). New therapeutic agents capable of modulating such processes are needed to foster neuroprotection. Here, the effect of an optimised NMDA receptor antagonist, UB-ALT-EV and memantine, as a gold standard, have been evaluated in 5XFAD mice. Following treatment with UB-ALT-EV, nor memantine, changes in the calcineurin (CaN)/NFAT pathway were detected. UB-ALT-EV increased neurotropic factors (Bdnf, Vgf and Ngf) gene expression. Treatments reduced astrocytic and microglial reactivity as revealed by glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (Iba-1) quantification. Interestingly, only UB-ALT-EV was able to reduce gene expression of Trem2, a marker of microglial activation and NF-κB. Pro-inflammatory cytokines Il-1β, Ifn-γ, Ccl2 and Ccl3 were down-regulated in UB-ALT-EV-treated mice but not in memantine-treated mice. Interestingly, the anti-inflammatory markers of the M2-migroglial phenotype, chitinase-like 3 (Ym1) and Arginase-1 (Arg1), were up-regulated after treatment with UB-ALT-EV. Since iNOS gene expression decreased after UB-ALT-EV treatment, a qPCR array containing 84 OS-related genes was performed. We found changes in Il-19, Il-22, Gpx6, Ncf1, Aox1 and Vim gene expression after UB-ALT-EV. Hence, our results reveal a robust effect on neuroinflammation and OS processes after UB-ALT-EV treatment, surpassing the memantine effect in 5XFAD.

Impact of Environmental Risk Factors on Mitochondrial Dysfunction, Neuroinflammation, Protein Misfolding, and Oxidative Stress in the Etiopathogenesis of Parkinson's Disease

As a prevalent progressive neurodegenerative disorder, Parkinson's disease (PD) is characterized by the neuropathological hallmark of the loss of nigrostriatal dopaminergic (DAergic) innervation and the appearance of Lewy bodies with aggregated α-synuclein. Although several familial forms of PD have been reported to be associated with several gene variants, most cases in nature are sporadic, triggered by a complex interplay of genetic and environmental risk factors. Numerous epidemiological studies during the past two decades have shown positive associations between PD and several environmental factors, including exposure to neurotoxic pesticides/herbicides and heavy metals as well as traumatic brain injury. Other environmental factors that have been implicated as potential risk factors for PD include industrial chemicals, wood pulp mills, farming, well-water consumption, and rural residence. In this review, we summarize the environmental toxicology of PD with the focus on the elaboration of chemical toxicity and the underlying pathogenic mechanisms associated with exposure to several neurotoxic chemicals, specifically 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, paraquat (PQ), dichloro-diphenyl-trichloroethane (DDT), dieldrin, manganese (Mn), and vanadium (V). Our overview of the current findings from cellular, animal, and human studies of PD provides information for possible intervention strategies aimed at halting the initiation and exacerbation of environmentally linked PD.

<em>Gardenia jasminoides</em> J. Ellis extract GJ-4 attenuates hyperlipidemic vascular dementia in rats via regulating PPAR-γ-mediated microglial polarization

Background

GJ-4 is extracted from Gardenia jasminoides J. Ellis (Fructus Gardenia) with crocin composition and has been demonstrated to improve memory deficits in several dementia models in our previous studies.

Objective

This study aimed to evaluate the effects of GJ-4 on hyperlipidemic vascular dementia (VD) and explore the underlying mechanisms.

Design

In the current study, we employed a chronic hyperlipidemic VD rat model by permanent bilateral common carotid arteries occlusion (2-VO) based on high-fat diet (HFD), which is an ideal model to mimic the clinical pathogenesis of human VD.

Results

Our results showed that GJ-4 could significantly reduce serum lipids level and improve cerebral blood flow in hyperlipidemic VD rats. Additionally, treatment with GJ-4 remarkedly ameliorated memory impairment and alleviated neuronal injury. Mechanistic investigation revealed that the neuroprotective effects of GJ-4 might be attributed to the inhibition of microglia-mediated neuro-inflammation via regulating the M1/M2 polarization. Our data further illustrated that GJ-4 could regulate the phenotype of microglia through activating the peroxisome proliferator-activated receptor-γ (PPAR-γ) and subsequently inhibited nuclear factor-κB (NF-κB) nuclear translocation and increased CCAAT/enhancer-binding protein β (C/EBPβ) expression.

Conclusion

Our results implied that GJ-4 might be a promising drug to improve VD through the regulation of microglial M1/M2 polarization and the subsequent inhibition of neuro-inflammation.

Zileuton, a 5-Lipoxygenase Inhibitor, Attenuates Haemolysate-Induced BV-2 Cell Activation by Suppressing the MyD88/NF-κB Pathway

M1 microglia induce neuroinflammation-related neuronal death in animal models of spontaneous subarachnoid haemorrhage. Zileuton is a 5-lipoxygenase inhibitor that reduces the levels of downstream pro-inflammatory cytokines. This study aimed to investigate whether zileuton inhibits microglial activation and describe its underlying mechanisms. BV-2 cells were exposed to 1 mg/mL haemolysate for 30 min, followed by treatment with different concentrations (5, 10, 15, or 20 μM) of zileuton for 24 h. The cells were then assessed for viability, polarisation, and protein expression levels. Haemolysate increases the viability of BV-2 cells and induces M1 polarisation. Subsequent exposure to high concentrations of zileuton decreased the viability of BV-2 cells, shifted the polarisation to the M2 phenotype, suppressed the expression of 5-lipoxygenase, decreased tumour necrosis factor α levels, and increased interleukin-10 levels. Furthermore, high concentrations of zileuton suppressed the expression of myeloid differentiation primary response protein 88 and reduced the phosphorylated-nuclear factor-kappa B (NF-kB)/NF-kB ratio. Therefore, phenotype reversal from M1 to M2 is a possible mechanism by which zileuton attenuates haemolysate-induced neuroinflammation after spontaneous subarachnoid haemorrhage.

JAK2/STAT3 pathway regulates microglia polarization involved in hippocampal inflammatory damage due to acute paraquat exposure

OBJECTIVE

To explore the effects of acute paraquat (PQ) exposure on the phenotypic polarization of hippocampal microglia and its mechanism.

METHODS

An acute PQ exposure rat model was established. Male SD rats were exposed to 0, 5, 25, and 50 mg/kg PQ, and brain hippocampal tissue was collected after 1, 3, and 7 days of exposure, respectively. Hippocampal pathological changes were examined by H&E staining, and immunohistochemistry (IHC) was used to detect changes in the number of Iba-1-positive cells, the average number of endpoints, and the average process length. The protein expression of Iba-1 was detected by western blotting. BV-2 microglia were treated with 0, 0.01, 0.025, 0.05, or 0.1 μmol/L PQ for 24 h. ELISA and western blotting assays were performed to detect the expression of TNF-α and IL-1β in vivo and in vitro. The M1 microglia marker iNOS, the M2 microglia marker Arg-1, and the p-JAK2 and p-STAT3 protein were detected by western blotting. JAK2/STAT3 pathway activation role in regulating microglia phenotypic polarization was further validated in vivo and in vitro by JAK2-specific inhibitor AG490 administration.

RESULTS

After acute PQ exposure, hippocampal neurons showed pathological changes such as loose arrangement and nuclear pyknosis, the number of Iba-1 positive cells and the expression of Iba-1 protein increased, and the average number of endpoints and average process length of microglia decreased. Histological examination revealed that compared with the control group, in the 50 mg/kg PQ group on the 3rd and 7th day, the expression of TNF-α, IL-1β, and iNOS significantly increased, while that of Arg-1 significantly decreased. p-JAK2 and p-STAT3 expression significantly increased in the 50 mg/kg PQ group on the 1st, 3rd, and 7th day. In vitro, compared with the control group, the expression of TNF-α, IL-1β, iNOS, p-JAK2, and p-STAT3 significantly increased, while Arg-1 expression was significantly reduced in the 0.025, 0.05, and 0.1 μmol/L PQ groups. After AG490 administration, the expression levels of p-JAK2, p-STAT3, iNOS, TNF-α, and IL-1β in the AG490 +PQ group were significantly inhibited in vivo and in vitro compared with the PQ-only group. On the contrary, Arg-1 expression was significantly increased.

CONCLUSION

Our results suggest that acute PQ exposure may induce M1-type polarization of hippocampal microglia by activating the JAK2/STAT3 pathway, which in turn releases pro-inflammatory factors such as TNF-α and IL-1β, leading to hippocampal inflammatory damage.

Adenosine A2A Receptor in Bone Marrow-Derived Cells Mediated Macrophages M2 Polarization via PPARγ-P65 Pathway in Chronic Hypoperfusion Situation

Background: The role of adenosine A_2A receptor (A_2AR) in the ischemic white matter damage induced by chronic cerebral hypoperfusion remains obscure. Here we investigated the role of A_2AR in the process of macrophage polarizations in the white matter damage induced by chronic cerebral hypoperfusion and explored the involved signaling pathways. Methods: We combined mouse model and macrophage cell line for our study. White matter lesions were induced in A_2AR knockout mice, wild-type mice, and chimeric mice generated by bone marrow cells transplantation through bilateral common carotid artery stenosis. Microglial/macrophage polarization in the corpus callosum was detected by immunofluorescence. For the cell line experiments, RAW264.7 macrophages were treated with the A_2AR agonist CHS21680 or A_2AR antagonist SCH58261 for 30 min and cultured under low-glucose and hypoxic conditions. Macrophage polarization was examined by immunofluorescence. The expression of peroxisome proliferator activated receptor gamma (PPARγ) and transcription factor P65 was examined by western blotting and real-time polymerase chain reaction (RT-PCR). Inflammatory cytokine factors were assessed by enzyme-linked immunosorbent assay (ELISA) and RT-PCR. Results: Both global A_2AR knockout and inactivation of A_2AR in bone marrow-derived cells enhanced M1 marker expression in chronic ischemic white matter lesions. Under low-glucose and hypoxic conditions, CGS21680 treatment promoted macrophage M2 polarization, increased the expression of PPARγ, P65, and interleukin-10 (IL-10) and suppressed the expression of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). The CGS21680-induced upregulation of P65 and IL-10 was abolished in macrophages upon PPARγ knockdown. The downregulation of TNF-α and IL-1β by CGS21680 was less affected by PPARγ knockdown. Conclusions: In the cerebral hypoperfusion induced white matter damage, A_2AR signaling in bone marrow-derived cells induces macrophage M2 polarization and increases the expression of the anti-inflammatory factor IL-10 via the PPARγ-P65 pathway, both of which might explain its neuroprotective effect.

Ellagic acid ameliorates paraquat-induced liver injury associated with improved gut microbial profile

Paraquat, a widely used herbicide, causes environmental pollution, and liver injury in humans and animals. As a natural compound in fruits, ellagic acid (EA) shows anti-inflammatory and antioxidant effects. This study examines the beneficial effects of dietary EA against the paraquat-induced hepatic injury and further explores the underlying molecular mechanisms using a piglet model. Post-weaning piglets are fed basal diet supplemented with 50 mg/kg, 100 mg/kg, or 200 mg/kg EA for 3 weeks. At week 2, hepatic injury is induced by 4 mg/kg paraquat followed by 7 days recovery. EA supplementation significantly mitigates paraquat-induced hepatic fibrosis, steatosis, and high apoptotic rate. In agreement, EA supplementation reduces serum pro-inflammatory levels, ameliorates inflammatory cells infiltration into hepatic tissue, which are associated with suppressed NF-κB signaling during paraquat exposure. In addition, EA supplementation significantly improves activities of antioxidative enzymes which were correlated with activated Nrf2/Keap 1 signaling during paraquat exposure. Furthermore, EA supplementation restores cecal microbial community during paraquat exposure. The protective effect of EA is strongly linked with increased relative abundance of Lactobacillus reuteri and Lactobacillus amylovorus. Taken together, EA supplementation effectively reduced the occurrence of hepatic oxidative damage and inflammation induced by paraquat through modulating cecal microbial communities, which provides a novel nutritional therapeutic strategy for hepatic injury.

Role of neurotoxicants in the pathogenesis of Alzheimer's disease: a mechanistic insight

Alzheimer's disease (AD) is the most conspicuous chronic neurodegenerative syndrome, which has become a significant challenge for the global healthcare system. Multiple studies have corroborated a clear association of neurotoxicants with AD pathogenicity, such as Amyloid beta (Aβ) proteins and neurofibrillary tangles (NFTs), signalling pathway modifications, cellular stress, cognitive dysfunctions, neuronal apoptosis, neuroinflammation, epigenetic modification, and so on. This review, therefore, aimed to address several essential mechanisms and signalling cascades, including Wnt (wingless and int.) signalling pathway, autophagy, mammalian target of rapamycin (mTOR), protein kinase C (PKC) signalling cascades, cellular redox status, energy metabolism, glutamatergic neurotransmissions, immune cell stimulations (e.g. microglia, astrocytes) as well as an amyloid precursor protein (APP), presenilin-1 (PSEN1), presenilin-2 (PSEN2) and other AD-related gene expressions that have been pretentious and modulated by the various neurotoxicants. This review concluded that neurotoxicants play a momentous role in developing AD through modulating various signalling cascades. Nevertheless, comprehension of this risk agent-induced neurotoxicity is far too little. More in-depth epidemiological and systematic investigations are needed to understand the potential mechanisms better to address these neurotoxicants and improve approaches to their risk exposure that aid in AD pathogenesis.Key messagesInevitable cascade mechanisms of how Alzheimer's Disease-related (AD-related) gene expressions are modulated by neurotoxicants have been discussed.Involvement of the neurotoxicants-induced pathways caused an extended risk of AD is explicited.Integration of cell culture, animals and population-based analysis on the clinical severity of AD is addressed.

Taurine protects dopaminergic neurons in paraquat-induced Parkinson's disease mouse model through PI3K/Akt signaling pathways

Taurine (Tau) is one of the most abundant amino acids in the brain and regulates physiological functions in the central nervous system, including anti-inflammatory effects. There is growing evidence that microglia-mediated neuro-inflammatory responses are an integral part of Parkinson's disease (PD) onset and progression. Among the many factors regulating the inflammatory response, phosphatidylinositol-3 kinase (PI3K) is susceptible to activation by a variety of cytokines and physicochemical factors, and subsequently recruits signaling proteins containing the pleckstrin homology structural domain to further regulate protein kinase B (AKT) expression involved in the regulation of the intracellular immune response and inflammatory response. Therefore, we established a PD mouse model using paraquat (PQ) intraperitoneal injection staining to explore the mechanism of Tau action on PI3K/AKT signaling pathway. Our study showed that PD mice with Tau intervention recovered motor and non-motor functions to some extent, and the number of dopaminergic (DAc) neurons in the substantia nigra and the level of dopamine (DA) secretion in the striatum were also significantly increased compared with the PQ-dyed group, and the protein content of PI3K and PDK-1 and the phosphorylation level of AKT were reduced in parallel with the reduction in the expression of microglia and related inflammatory factors. In conclusion, our results suggest that Tau may regulate microglia-mediated inflammatory responses through inhibition of the PI3K/AKT pathway in the midbrain of PD mice, thereby reducing DAc neurons damage.

Vagus nerve stimulation mediates microglia M1/2 polarization via inhibition of TLR4 pathway after ischemic stroke

Ischemic stroke is the leading cause of death and disability. Microglia are polarized toward the proinflammatory M1 phenotype and neuroprotective M2 phenotype after stroke and play an important role in the pathological process of ischemic stroke. Emerging research suggests that vagus nerve stimulation (VNS) can mediate microglia polarization after ischemic stroke and may serve as a potential treatment for ischemic stroke. However, the mechanism by which VNS mediates microglia polarization remains unclear. In this study, we aimed to investigate the underlying mechanism. Sprague-Dawley rats were randomly divided into the sham, ischemic stroke, ischemic stroke + VNS, ischemic stroke + VNS + lentivirus (LV)-TLR4 and ischemic stroke + VNS + LV-CON groups. LV was injected into the lateral ventricles of the rats 14 days before ischemic stroke surgery, and VNS was administered after 30 min of occlusion. We assessed the infarct volume, neurological scores, the TLR4/MyD88/NF-κB protein level and microglia polarization after 3 days of reperfusion. Our results revealed that VNS can promote M2 microglia polarization and inhibit M1 microglia polarization to alleviate brain injury via inhibition of the TLR4/MyD88/NF-κB pathway in microglia in the acute stage of stroke.

The effects of metallothionein in paraquat-induced Parkinson disease model of zebrafish

INTRODUCTION

Parkinson's disease (PD) is the second most common neurodegenerative disease caused by selective degeneration of dopaminergic neurons in the substantia nigra. Metallothionein has been shown to act as a neuroprotectant in various brain injury. Thus, this study aims to identify the effects of full-length human metallothionein 2 peptide (hMT2) in paraquat-induced brain injury in the zebrafish.

METHODOLOGY

A total of 80 adult zebrafish were divided into 4 groups namely control, paraquat-treated, pre-hMT2-treated, and post-hMT2-treated groups. Fish were treated with paraquat intraperitoneally every 3 days for 15 days. hMT2 were injected intracranially on day 0 (pre-treated group) and day 16 (post-treated group). Fish were sacrificed on day 22 and the brains were collected for qPCR, ELISA and immunohistochemistry analysis.

RESULTS

qPCR analysis showed that paraquat treatment down-regulated the expression of genes related to dopamine activity and biosynthesis (dat and th1) and neuroprotective agent (bdnf). Paraquat treatment also up-regulated the expression of the mt2, smtb and proinflammatory genes (il-1α, il-1β, tnf-α and cox-2). hMT2 treatment was able to reverse the effects of paraquat. Lipid peroxidation decreased in the paraquat and pre-hMT2-treated groups. However, lipid peroxidation increased in the post-hMT2-treated group. Paraquat treatment also led to a reduction of dopaminergic neurons while their numbers showed an increase following hMT2 treatment.

CONCLUSION

Paraquat has been identified as one of the pesticides that can cause the death of dopaminergic neurons and affect dopamine biosynthesis. Treatment with exogenous hMT2 could reverse the effects of paraquat in the zebrafish brain.

Neuron-Glia Crosstalk Plays a Major Role in the Neurotoxic Effects of Ketamine via Extracellular Vesicles

Background: There is a compelling evidence from animal models that early exposure to clinically relevant general anesthetics (GAs) interferes with brain development, resulting in long-lasting cognitive impairments. Human studies have been inconclusive and are challenging due to numerous confounding factors. Here, we employed primary human neural cells to analyze ketamine neurotoxic effects focusing on the role of glial cells and their activation state. We also explored the roles of astrocyte-derived extracellular vesicles (EVs) and different components of the brain-derived neurotrophic factor (BDNF) pathway.

Methods: Ketamine effects on cell death were analyzed using live/dead assay, caspase 3 activity and PARP-1 cleavage. Astrocytic and microglial cell differentiation was determined using RT-PCR, ELISA and phagocytosis assay. The impact of the neuron-glial cell interactions in the neurotoxic effects of ketamine was analyzed using transwell cultures. In addition, the role of isolated and secreted EVs in this cross-talk were studied. The expression and function of different components of the BDNF pathway were analyzed using ELISA, RT-PCR and gene silencing.

Results: Ketamine induced neuronal and oligodendrocytic cell apoptosis and promoted pro-inflammatory astrocyte (A1) and microglia (M1) phenotypes. Astrocytes and microglia enhanced the neurotoxic effects of ketamine on neuronal cells, whereas neurons increased oligodendrocyte cell death. Ketamine modulated different components in the BDNF pathway: decreasing BDNF secretion in neurons and astrocytes while increasing the expression of p75 in neurons and that of BDNF-AS and pro-BDNF secretion in both neurons and astrocytes. We demonstrated an important role of EVs secreted by ketamine-treated astrocytes in neuronal cell death and a role for EV-associated BDNF-AS in this effect.

Conclusions: Ketamine exerted a neurotoxic effect on neural cells by impacting both neuronal and non-neuronal cells. The BDNF pathway and astrocyte-derived EVs represent important mediators of ketamine effects. These results contribute to a better understanding of ketamine neurotoxic effects in humans and to the development of potential approaches to decrease its neurodevelopmental impact.

Microglial Phenotypic Transition: Signaling Pathways and Influencing Modulators Involved in Regulation in Central Nervous System Diseases

Microglia are macrophages that reside in the central nervous system (CNS) and belong to the innate immune system. Moreover, they are crucially involved in CNS development, maturation, and aging; further, they are closely associated with neurons. In normal conditions, microglia remain in a static state. Upon trauma or lesion occurrence, microglia can be activated and subsequently polarized into the pro-inflammatory or anti-inflammatory phenotype. The phenotypic transition is regulated by numerous modulators. This review focus on the literature regarding the modulators and signaling pathways involved in regulating the microglial phenotypic transition, which are rarely mentioned in other reviews. Hence, this review provides molecular insights into the microglial phenotypic transition, which could be a potential therapeutic target for neuroinflammation.

Mitochondrial dysfunction-induced H3K27 hyperacetylation perturbs enhancers in Parkinson's disease

Mitochondrial dysfunction is a major pathophysiological contributor to the progression of Parkinson’s disease (PD); however, whether it contributes to epigenetic dysregulation remains unknown. Here, we show that both chemically and genetically driven mitochondrial dysfunctions share a common mechanism of epigenetic dysregulation. Under both scenarios, lysine 27 acetylation of likely variant H3.3 (H3.3K27ac) increased in dopaminergic neuronal models of PD, thereby opening that region to active enhancer activity via H3K27ac. These vulnerable epigenomic loci represent potential transcription factor motifs for PD pathogenesis. We further confirmed that mitochondrial dysfunction induces H3K27ac in ex vivo and in vivo (MitoPark) neurodegenerative models of PD. Notably, the significantly increased H3K27ac in postmortem PD brains highlights the clinical relevance to the human PD population. Our results reveal an exciting mitochondrial dysfunction-metabolism-H3K27ac-transcriptome axis for PD pathogenesis. Collectively, the mechanistic insights link mitochondrial dysfunction to epigenetic dysregulation in dopaminergic degeneration and offer potential new epigenetic intervention strategies for PD.

Targeting Neuroinflammation via Purinergic P2 Receptors for Disease Modification in Drug-Refractory Epilepsy

Treatment of epilepsy remains a clinical challenge, with >30% of patients not responding to current antiseizure drugs (ASDs). Moreover, currently available ASDs are merely symptomatic without altering significantly the progression of the disease. Inflammation is increasingly recognized as playing an important role during the generation of hyperexcitable networks in the brain. Accordingly, the suppression of chronic inflammation has been suggested as a promising therapeutic strategy to prevent epileptogenesis and to treat drug-refractory epilepsy. As a consequence, a strong focus of ongoing research is identification of the mechanisms that contribute to sustained inflammation in the brain during epilepsy and whether these can be targeted. ATP is released in response to several pathological stimuli, including increased neuronal activity within the central nervous system, where it functions as a neuro- and gliotransmitter. Once released, ATP activates purinergic P2 receptors, which are divided into metabotropic P2Y and ionotropic P2X receptors, driving inflammatory processes. Evidence from experimental models and patients demonstrates widespread expression changes of both P2Y and P2X receptors during epilepsy, and critically, drugs targeting both receptor subtypes, in particular the P2Y₁ and P2X₇ subtypes, have been shown to possess both anticonvulsive and antiepileptic potential. This review provides a detailed summary of the current evidence suggesting ATP-gated receptors as novel drug targets for epilepsy and discusses how P2 receptor–driven inflammation may contribute to the generation of seizures and the development of epilepsy.

How Macrophages Become Transcriptionally Dysregulated: A Hidden Impact of Antitumor Therapy

Tumor-associated macrophages (TAMs) are the essential components of the tumor microenvironment. TAMs originate from blood monocytes and undergo pro- or anti-inflammatory polarization during their life span within the tumor. The balance between macrophage functional populations and the efficacy of their antitumor activities rely on the transcription factors such as STAT1, NF-κB, IRF, and others. These molecular tools are of primary importance, as they contribute to the tumor adaptations and resistance to radio- and chemotherapy and can become important biomarkers for theranostics. Herein, we describe the major transcriptional mechanisms specific for TAM, as well as how radio- and chemotherapy can impact gene transcription and functionality of macrophages, and what are the consequences of the TAM-tumor cooperation.

Anti-inflammatory effect of IL-1ra-loaded dextran/PLGA microspheres on Porphyromonas gingivalis lipopolysaccharide-stimulated macrophages in vitro and in vivo in a rat model of periodontitis

Periodontitis is a multifactorial chronic infectious disease leading to a host immune response involving inflammatory cytokines, especially IL-1β, which is the main reason for further developing this disease. IL-1 receptor antagonist (IL-1ra) binds IL-1 receptor, inhibiting IL-1β signaling and reducing the levels of other cytokines closely related to periodontitis, such as IL-6 and TNF-α. Therefore, the use of IL-1ra to inhibit periodontitis development in a system, ensuring its sustained release, might be an effective way to combat this disease. Hence, in this study, a novel IL-1ra-loaded dextran/PLGA microsphere was developed to allow the sustained release of IL-1ra and enhance the anti-inflammatory properties. Therefore, this study's purposes were to develop a novel periodontal treatment for inhibition and treatment of periodontitis and evaluate the sustained-release effect and anti-inflammatory properties of IL-1ra-loaded dextran/PLGA microspheres in vitro by cell experiments and in vivo by animal experiments. The results showed that IL-1ra-loaded dextran/PLGA microspheres were non-toxic both in vitro and in vivo and could be used as a safe and effective treatment. In addition, these microspheres could significantly prolong the half-life of IL-1ra drug, exerting a useful anti-inflammatory effect in macrophages stimulated with P. gingivalis lipopolysaccharide and in rats with periodontitis. In conclusion, IL-1ra-loaded dextran/PLGA microsphere might be a useful tool to combat periodontal disease.

Arecanut (Areca catechu L.) Seed Polyphenol-Ameliorated Osteoporosis by Altering Gut Microbiome via LYZ and the Immune System in Estrogen-Deficient Rats

Polyphenol can improve osteoporosis and is closely associated with gut microbiota, while the mechanism and the relationship among polyphenol, osteoporosis, and gut microbiota colonization remain unclear. Here, an osteoporosis rat model established by ovariectomy was employed to investigate the improving mechanism of arecanut (Areca catechu L.) seed polyphenol (ACP) on osteoporosis by regulating gut microbiota. We analyzed the bone microstructure, Paneth cells, regulating microbial protein (lysozyme (LYZ)), proinflammatory cytokines, macrophage infiltration levels, and gut microbial communities in a rat. ACP improved the trabecular microstructure compared to OVX, including the increased trabecular number (Tb.N) (P < 0.01) and trabecular thickness (Tb.Th) (P < 0.001) and decreased trabecular separation (Tb.Sp) (P < 0.01). At the phylum level, Bacteroidetes was increased after ovariectomy (P < 0.001) and Firmicutes and Proteobacteria were increased in ACP (P < 0.001). Antiosteoporosis groups with lower LYZ and Paneth cells (P < 0.001) showed that the microbiota Alistipes, which have a negative effect on bone metabolism were decreased in ACP (P < 0.001). Altogether, these studies showed that the estrogen deficiency could induce the shedding of Paneth cells, which leads to the decrease of LYZ, while ACP could increase the LYZ expression by maintaining the population of Paneth cells in an estrogen-deficient host, which were implicated in gut microbiota regulation and improved osteoporosis by controlling the inflammatory reaction.

Paraquat-activated BV-2 microglia induces neuroinflammatory responses in the neuron model through NF-κB signaling pathway

Paraquat (PQ), a non-selective contact herbicide, has been generally accepted as one of the environmental neurotoxicants. Despite the direct evidence that PQ could induce inflammation responses in microglia, little is known about the effects of the inflammatory microglia on neurons. Thus in the present study, mouse primary cortical neurons and PC12 cells, widely-used in vitro neuron models for neurotoxicity research were applied to investigate the neuroinflammatory effects of PQ-activated microglia on neurons. We observed that the secretion levels of TNF-α and IL-6 in PC12 cells were markedly increased upon treatment with the supernatants of inflammatory BV2 microglia, and NF-κB p65 protein expression was also elevated. Specific inhibition of NF-κB by PDTC dramatically attenuated the increase of TNF-α and IL-6 release. These results suggested that PQ-induced inflammatory microglia exerts secondary inflammatory effects on neurons through activation of NF-κB pathway.

Telocytes Enhances M1 Differentiation and Phagocytosis While Inhibits Mitochondria-Mediated Apoptosis Via Activation of NF-κB in Macrophages

Telocytes (TCs), which are a recently discovered interstitial cell type present in various organs and tissues, perform multiple biological functions and participate in extensive crosstalk with neighboring cells. Endometriosis (EMs) is a gynecological disease characterized by the presence of viable endometrial debris and impaired macrophage phagocytosis in the peritoneal environment. Here, CD34/vimentin-positive TCs were co-cultured with RAW264.7 cells in vitro. M1/M2 differentiation-related markers were detected; phagocytosis, energy metabolism, proliferation, apoptosis, and pathway mechanisms were studied; and the mitochondrial membrane potential (ΔΨm) was measured. Furthermore, in an EMs mouse model, the differentiation of macrophages in response to treatment with TC-conditioned medium (TCM) in vivo was studied. The results showed that upon in vitro co-culture with TCM, RAW264.7 cells differentiated more toward the M1 phenotype with enhancement of phagocytosis, increase in energy metabolism and proliferation owing to reduced the loss of ΔΨm, and suppression of dexamethasone-induced apoptosis. Further, along with the activation of NF-κB, Bcl-2 and Bcl-xl, the expression of Bax, cleaved-caspase9, and cleaved-caspase3 reduced in RAW264.7 cells. In addition, the M1 subtype was found to be the dominant phenotype among tissue and peritoneal macrophages in the EMs model subjected to in vivo TCM treatment. In conclusion, TCs enhanced M1 differentiation and phagocytosis while inhibiting apoptosis via the activation of NF-κB in macrophages, which potentially inhibited the onset of EMs. Our findings provide a potential research target and the scope for developing a promising therapeutic strategy for EMs.

Decoding the role of zebrafish neuroglia in CNS disease modeling

Neuroglia, including microglia and astrocytes, is a critical component of the central nervous system (CNS) that interacts with neurons to modulate brain activity, development, metabolism and signaling pathways. Thus, a better understanding of the role of neuroglia in the brain is critical. Complementing clinical and rodent data, the zebrafish (Danio rerio) is rapidly becoming an important model organism to probe the role of neuroglia in brain disorders. With high genetic and physiological similarity to humans and rodents, zebrafish possess some common (shared), as well as some specific molecular biomarkers and features of neuroglia development and functioning. Studying these common and zebrafish-specific aspects of neuroglia may generate important insights into key brain mechanisms, including neurodevelopmental, neurodegenerative, neuroregenerative and neurological processes. Here, we discuss the biology of neuroglia in humans, rodents and fish, its role in various CNS functions, and further directions of translational research into the role of neuroglia in CNS disorders using zebrafish models.

Paraquat increases Interleukin-1β in hippocampal dentate gyrus to impair hippocampal neurogenesis in adult mice

Paraquat (1,1'-dimethyl-4,4'-bipyridium dichloride, PQ), a non-selective and efficient herbicide, causes neuroinflammation, neurodegeneration and memory dysfunction. However, adverse effects of PQ on the neuroimmune interactions have rarely been investigated. Female adult C57/BL6 mice were divided into 3 groups and treated with PQ (intraperitoneal injection, 1 mg/kg or 5 mg/kg) or the vehicle (an equivalent volume of 0.9% saline) every two days, at day 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, for a total of 14 doses. We evaluated blood-brain barrier (BBB) integrity and PQ concentrations during the course of PQ exposure and tested interleukin-1β (IL-1β) concentrations in dentate gyrus (DG) after 28 days PQ exposure. In addition, memory function, neural stem cells (NSCs) proliferation, neurogenesis and microglia polarization were analyzed after PQ exposure. Furthermore, mice were intraperitoneal injections of anti-IL-1β during 5 mg/kg PQ exposure to test the rule of IL-1β. Blood-brain barrier (BBB) permeability and PQ concentrations increased gradually during PQ exposure (n = 6). Moreover, memory function, NSCs proliferation and neurogenesis were impaired after 5 mg/kg PQ exposure (n = 6). Further analyses revealed that 'classically' activated (M1) microglia and IL-1β concentrations in DG were increased after 5 mg/kg PQ treatment (n = 6). Moreover, we found that neutralization of IL-1β partly restored PQ-induced NSCs impairments and memory dysfunction (n = 6). In conclusion, our results revealed that PQ induced NSCs impairments and memory dysfunction in adult mice, which was related to the release of IL-1β by M1-polarized microglia in DG. These findings may help understand the neurotoxic effect of PQ.

Depletion of NK cells attenuates paraquat-induced acute lung injury by manipulating macrophage polarization

Acute lung injury is the main causative factor in paraquat dichloride (PQ)-induced mortality. The innate immune system-triggered detrimental inflammatory cascade plays a vital role in PQ-induced acute lung injury. However, the role of natural killer (NK) cells, which are essential for innate response, in PQ-induced acute lung injury remains largely unknown. Here, we found that in an acute PQ poisoning model, depletion of NK cells attenuated PQ-induced lung injury by inhibiting macrophage polarization towards the M1 type. Specifically, the percentages of NK cells were reduced in the lung, spleen, and peripheral blood in a murine model of acute PQ poisoning. NK cells were aberrantly activated, evidenced by upregulation of the activating markers CD69, CD107a, and NKG2D and downregulation of the inhibitive marker KLRG1. Further, NK-specific depletion in mice greatly prolonged the survival time and ameliorated reactive oxygen species-induced damage following PQ treatment compared with the control group. Importantly, NK cell depletion alleviated macrophage and neutrophil infiltration in the lung and reversed PQ induced-macrophage polarization towards the pro-inflammatory M1 type. Our study demonstrates a crucial role of NK cells and NK cell-to-macrophage interaction in PQ-induced acute lung injury.

Role of Innate Immune Receptor TLR4 and its endogenous ligands in epileptogenesis

Understanding the interplay between the innate immune system, neuroinflammation, and epilepsy might offer a novel perspective in the quest of exploring new treatment strategies. Due to the complex pathology underlying epileptogenesis, no disease-modifying treatment is currently available that might prevent epilepsy after a plausible epileptogenic insult despite the advances in pre-clinical and clinical research. Neuroinflammation underlies the etiopathogenesis of epilepsy and convulsive disorders with Toll-like receptor (TLR) signal transduction being highly involved. Among TLR family members, TLR4 is an innate immune system receptor and lipopolysaccharide (LPS) sensor that has been reported to contribute to epileptogenesis by regulating neuronal excitability. Herein, we discuss available evidence on the role of TLR4 and its endogenous ligands, the high mobility group box 1 (HMGB1) protein, the heat shock proteins (HSPs) and the myeloid related protein 8 (MRP8), in epileptogenesis and post-traumatic epilepsy (PTE). Moreover, we provide an account of the promising findings of TLR4 modulation/inhibition in experimental animal models with therapeutic impact on seizures.

DHZCP Modulates Microglial M1/M2 Polarization via the p38 and TLR4/NF-κB Signaling Pathways in LPS-Stimulated Microglial Cells

Intracerebral hemorrhage (ICH) is a disease with a significantly high rate of morbidity, mortality and disability. Inhibition of inflammation is considered a potential strategy for improving the clinical symptoms induced by ICH. The hallmark of neuroinflammation is microglial activation. Microglia can polarize into either the classically activated M1 (proinflammatory) phenotype, exacerbating neuronal damage, or the alternatively activated M2 (antiinflammatory) phenotype, exerting neuroprotection and promoting neuronal recovery. Promoting microglial polarization to the M2 phenotype may be a viable strategy for treating neuroinflammation. Several studies have indicated that promoting blood circulation and removing blood stasis exhibits therapeutic effects on intracerebral hemorrhage. Dahuang Zhechong Pill (DHZCP), a classical recipe that promotes blood circulation and removes blood stasis, has been reported to improve the clinical outcome of ICH. DHZCP has been shown to exert antiinflammatory effects. However, the detailed antiinflammatory mechanism of DHZCP in ICH has rarely been investigated. In this study, DHZCP inhibited lipopolysaccharide (LPS)-induced M1 microglial activation. DHZCP exerted antiinflammatory effects, by inhibiting LPS-induced M1 proinflammatory cytokine (TNF-α and IL-6), and iNOS production and increasing M2 antiinflammatory cytokine (IL-10) production. DHZCP also switched microglial polarization from M1 to M2, as indicated by significantly increased expression of M2 polarization markers (CD209, and CD206) and markedly decreased expression of an M1 polarization marker (CD54). In addition, DHZCP inhibited p38 and TLR4/NF-κB signaling activation, as demonstrated by inhibition of LPS-induced increases in p-p38, TLR4 and nuclear factor kappa B p-65 (NF-κB p-65) protein expression. Taken together, DHZCP modulates microglial M1/M2 polarization via the p38 and TLR4/NF-κB signaling pathways to confer antiinflammatory effects.

Knockdown of TLR4 Represses the Paraquat-Induced Neuroinflammation and Microglial M1 Polarization

Paraquat (PQ) is associated with multiple nervous system disorders including Parkinson's disease. Despite the evidence that PQ could induce inflammatory responses in the central nervous system and largely contribute to neurotoxicity, the mechanisms of PQ-induced neuroinflammation are not yet fully understood. Toll-like receptor 4 (TLR4) could recognize various pathogens and initiate inflammation processes. Therefore, we investigated the role of TLR4 in PQ-induced neuroinflammation by using murine microglial immortalized BV-2 cell line. Normal microglia and TLR4-knockdown microglia were treated with PQ to evaluate signal transduction molecular expression, inflammatory responses, and microglial functions. Compared with normal microglia, PQ-induced production of pro-inflammatory cytokines was significantly reduced in TLR4-knockdown microglia. Levels of M1 markers were decreased, while levels of M2 markers were increased upon PQ exposure, confirming that TLR4 depletion inhibited the microglial M1 polarization. Besides, the migration and phagocytosis capability reduced by PQ were to some extent recovered in TLR4-knockdown microglia. Taken together, our results suggested that TLR4 mediated the neuroinflammatory responses in microglia and the depletion of TLR4 protects against PQ neurotoxicity.

Integrin CD11b mediates locus coeruleus noradrenergic neurodegeneration in a mouse Parkinson's disease model

BACKGROUND

The loss of locus coeruleus noradrenergic (LC/NE) neurons in the brainstem is reported in multiple neurodegenerative disorders, including Parkinson's disease (PD). However, the mechanisms remain unclear. Strong evidence suggested that microglia-mediated neuroinflammation contributes to neurodegeneration in PD. We recently recognized integrin CD11b, the α-chain of macrophage antigen complex-1 (Mac-1, also called CR3), as a key regulator for microglial activation. However, whether CD11b is involved in LC/NE neurodegeneration in PD remains to be investigated.

METHODS

LC/NE neurodegeneration and microglial activation were compared between wild type (WT) and CD11b KO mice after treated with paraquat and maneb, two pesticides that widely used to create PD model. The role of NLRP3 inflammasome in CD11b-mediated microglial dysfunction and LC/NE neurodegeneration was further explored. LC/NE neurodegeneration, microglial phenotype, and NLRP3 inflammasome activation were determined by using Western blot, immunohistochemistry, and RT-PCR technologies.

RESULTS

Paraquat and maneb co-exposure elevated the expressions of CD11b in the brainstem of mice, and CD11b knockout significantly reduced LC/NE neurodegeneration induced by paraquat and maneb. Mitigated microglial activation and gene expressions of proinflammatory cytokines were also observed in paraquat and maneb-treated CD11b^-/- mice. Mechanistically, CD11b-mediated NLRP3 inflammasome activation contributes to paraquat and maneb-induced LC/NE neurodegeneration. Compared with WT controls, CD11b deficiency reduced paraquat and maneb-induced NLRP3 expression, caspase-1 activation, and interleukin-1β production in mice. Furthermore, inhibition of NLRP3 inflammasome by glybenclamide, a sulfonylurea inhibitor of NLRP3 inflammasome, was found to be able to suppress microglial proinflammatory activation and nuclear factor-κB activation induced by paraquat and maneb. Moreover, reduced reactive oxygen species production, NADPH oxidase, and inducible nitric oxide synthase expressions as well as 4-hydroxynonenal and malondialdehyde levels were detected in combined glybenclamide and paraquat and maneb-treated mice compared with paraquat and maneb alone group. Finally, we found that glybenclamide treatment ameliorated LC/NE neurodegeneration and α-synuclein aggregation in paraquat and maneb-treated mice.

CONCLUSION

Our findings suggested that CD11b mediates LC/NE neurodegeneration through NLRP3 inflammation-dependent microglial proinflammatory activation in a two pesticide-induced mouse PD model, providing a novel insight into the immune pathogenesis of LC/NE neuronal damage in related disorders.

Modulators of microglia activation and polarization in ischemic stroke (Review)

Ischemic stroke is one of the leading causes of mortality and disability worldwide. However, there is a current lack of effective therapies available. As the resident macrophages of the brain, microglia can monitor the microenvironment and initiate immune responses. In response to various brain injuries, such as ischemic stroke, microglia are activated and polarized into the proinflammatory M1 phenotype or the anti-inflammatory M2 phenotype. The immunomodulatory molecules, such as cytokines and chemokines, generated by these microglia are closely associated with secondary brain damage or repair, respectively, following ischemic stroke. It has been shown that M1 microglia promote secondary brain damage, whilst M2 microglia facilitate recovery following stroke. In addition, autophagy is also reportedly involved in the pathology of ischemic stroke through regulating the activation and function of microglia. Therefore, this review aimed to provide a comprehensive overview of microglia activation, their functions and changes, and the modulators of these processes, including transcription factors, membrane receptors, ion channel proteins and genes, in ischemic stroke. The effects of autophagy on microglia polarization in ischemic stroke were also reviewed. Finally, future research areas of ischemic stroke and the implications of the current knowledge for the development of novel therapeutics for ischemic stroke were identified.

Oleanolic acid administration alleviates neuropathic pain after a peripheral nerve injury by regulating microglia polarization-mediated neuroinflammation

Neuropathic pain caused by a peripheral nerve injury constitutes a great challenge in clinical treatments due to the unsatisfactory efficacy of the current strategy. Microglial activation-mediated neuroinflammation is a major characteristic of neuropathic pain. Oleanolic acid is a natural triterpenoid in food and medical plants, and fulfills pleiotropic functions in inflammatory diseases. Nevertheless, its role in neuropathic pain remains poorly elucidated. In the current study, oleanolic acid dose-dependently suppressed LPS-evoked IBA-1 expression (a microglial marker) without cytotoxicity to microglia, suggesting the inhibitory efficacy of oleanolic acid in microglial activation. Moreover, oleanolic acid incubation offset LPS-induced increases in the iNOS transcript and NO releases from microglia, concomitant with the decreases in pro-inflammatory cytokine transcripts and production including IL-6, IL-1β, and TNF-α. Simultaneously, oleanolic acid shifted the microglial polarization from the M1 phenotype to the M2 phenotype upon LPS conditions by suppressing LPS-induced M1 marker CD16, CD86 transcripts, and enhancing the M2 marker Arg-1 mRNA and anti-inflammatory IL-10 levels. In addition, the LPS-induced activation of TLR4-NF-κB signaling was suppressed in the microglia after the oleanolic acid treatment. Restoring this signaling by the TLR4 plasmid transfection overturned the suppressive effects of oleanolic acid on microglial polarization-evoked inflammation. In vivo, oleanolic acid injection alleviated allodynia and hyperalgesia in SNL-induced neuropathic pain mice. Concomitantly, oleanolic acid facilitated microglial polarization to M2, accompanied by inhibition in inflammatory cytokine levels and activation of TLR4-NF-κB signaling. Collectively, these findings confirm that oleanolic acid may ameliorate neuropathic pain by promoting microglial polarization from pro-inflammatory M1 to anti-inflammatory M2 phenotype via the TLR4-NF-κB pathway, thereby indicating its usefulness as therapeutic intervention in neuropathic pain.

Neuropathic pain caused by a peripheral nerve injury constitutes a great challenge in clinical treatments due to the unsatisfactory efficacy of the current strategy.

H2S alleviates renal injury and fibrosis in response to unilateral ureteral obstruction by regulating macrophage infiltration via inhibition of NLRP3 signaling

Renal fibrosis is a key pathological feature in chronic kidney diseases (CKDs). Dysregulation of hydrogen sulfide (H₂S) homeostasis is implicated in the pathogenesis of CKDs. Here, C57/BL6 mice were allocated to Sham and unilateral ureteral obstruction (UUO) groups, which were treated with NaHS or NLRP3 inflammasome inhibitor 16673-34-0 for 3-14 days. UUO mice displayed downregulation of H₂S production and increased macrophage infiltration in obstructed kidneys. H₂S donor NaHS treatment attenuated renal damage and fibrosis and inhibited M1 and M2 macrophage infiltration. NLPR3 inflammasome was activated and levels of phosphorylated nuclear factor κB (NF-κB) p65 subunit, phosphorylated signal transducer and activator of transcription 6 (STAT6) and interleukin (IL)-4 protein were increased in the kidneys after UUO. NLRP3 inhibitor inactivated NF-κB and IL-4/STAT6 signaling, suppressed M1 and M2 macrophage infiltration and attenuated renal damage and fibrosis in UUO mice. NaHS treatment also suppressed NLRP3, NF-κB and IL-4/STAT6 activation in the obstructed kidneys. In conclusion, the therapeutic effects of H₂S on UUO-induced renal injury and fibrosis are at least in part by inhibition of M1 and M2 macrophage infiltration. H₂S suppresses NLRP3 activation and subsequently inactivates NF-κB and IL-4/STAT6 signaling, which may contribute to the anti-inflammatory and anti-fibrotic effects of H₂S.

Curcumin Mitigates Neuro-Inflammation by Modulating Microglia Polarization Through Inhibiting TLR4 Axis Signaling Pathway Following Experimental Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) elicits destruction of neuronal cells and neurological function, which is exacerbated by neuro-inflammation in EBI, and toll-like receptor 4 (TLR4) plays an important role in inflammatory cascade via modulation microglia polarization. Curcumin (Cur), as a natural phytochemical compound, has the potential characteristics on anti-inflammatory and microglia phenotype transformation. In this study, we verified the hypothesis curcumin promotes M2 polarization to inhibiting neuro-inflammation, which through suppressing TLR4 signaling pathway after SAH. In tlr4^–/– mice and wild type (WT) subjected to prechiasmatic cistern blood injection, Western blotting, brain water content, neurological score, enzyme-linked immunosorbent assay (ELISA) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were performed to investigate the role of TLR4 on neuro-inflammation response and microglia polarization. Curcumin with three different concentrations (50 mg/kg, 100 mg/kg and 200 mg/kg) were injected intraperitoneally (i.p.) at 15 min after SAH. The levels of TLR4, myeloid differentiation factor 88 (MyD88), nuclear factor- κB (NF-κB), Iba-1, CD86, CD206 and pro/anti-inflammation cytokines were measured by Western blotting and immunofluorescence staining at 24 h after SAH. SAH induction increased the protein levels of TLR4, pro-inflammation cytokines and proportion of M1 phenotype. Curcumin with 100 mg/kg treatment dramatically inhibited the release of pro-inflammatory mediators, and elevated the protein levels of anti-inflammatory cytokines and promoted microglia switch to M2. Meanwhile, curcumin treatment also decreased the expressions of TLR4, Myd88 and NF-κB at 24 h post SAH. TLR4 deficiency ameliorated brain water content, neurological deficit and reduced pro-inflammation cytokines after SAH. Moreover, curcumin treatment in tlr4^–/– mice further induced M2 polarization, while had no statistic difference on brain water content and neurological score at 24 h post SAH. Our results indicated that curcumin treatment alleviated neuro-inflammation response through promoting microglia phenotype shift toward M2, and which might inhibiting TLR4/MyD88/NF-κB signaling pathway after SAH.