Microglia-mediated Neuroinflammatory Response Research Articles

Human adipose tissue-derived stem cell extracellular vesicles attenuate ocular hypertension-induced retinal ganglion cell damage by inhibiting microglia- TLR4/MAPK/NF-κB proinflammatory cascade signaling

Microglia-mediated neuroinflammatory responses are recognized as a predominant factor during high intraocular pressure (IOP)-induced retinal and optic nerve injury along with potential therapeutic targets for the disease. Our previous research indicated that mesenchymal stem cell (MSC) treatment could reduce high IOP-induced neuroinflammatory responses through the TLR4 pathway in a rat model without apparent cell replacement and differentiation, suggesting that the anti-neuroinflammatory properties of MSCs are potentially mediated by paracrine signaling. This study aimed to evaluate the anti-neuroinflammatory effect of human adipose tissue-derived extracellular vesicles (ADSC-EVs) in microbead-induced ocular hypertension (OHT) animals and to explore the underlying mechanism since extracellular vesicles (EVs) are the primary transporters for cell secretory action. The anti-neuroinflammatory effect of ADSC-EVs on LPS-stimulated BV-2 cells in vitro and OHT-induced retinal and optic nerve injury in vivo was investigated. According to the in vitro research, ADSC-EV treatment reduced LPS-induced microglial activation and the TLR4/NF-κB proinflammatory cascade response axis in BV-2 cells, such as CD68, iNOS, TNF-α, IL-6, and IL-1β, TLR4, p-38 MAPK, NF-κB. According to the in vivo data, intravitreal injection of ADSC-EVs promoted RGC survival and function, reduced microglial activation, microglial-derived neuroinflammatory responses, and TLR4/MAPK/NF-κB proinflammatory cascade response axis in the OHT mice. Our findings provide preliminary evidence for the RGC protective and microglia-associated neuroinflammatory reduction effects of ADSC-EVs by inhibiting the TLR4/MAPK/NF-κB proinflammatory cascade response in OHT mice, indicating the therapeutic potential ADSC-EVs or adjunctive therapy for glaucoma.

Microglia trigger the structural plasticity of GABAergic neurons in the hippocampal CA1 region of a lipopolysaccharide-induced neuroinflammation model

It is well-established that microglia-mediated neuroinflammatory response involves numerous neuropsychiatric and neurodegenerative diseases. While the role of microglia in excitatory synaptic transmission has been widely investigated, the impact of innate immunity on the structural plasticity of GABAergic inhibitory synapses is not well understood. To investigate this, we established an inflammation model using lipopolysaccharide (LPS) and observed a prolonged microglial response in the hippocampal CA1 region of mice, which was associated with cognitive deficits in the open field test, Y-maze test, and novel object recognition test. Furthermore, we found an increased abundance of GABAergic interneurons and GABAergic synapse formation in the hippocampal CA1 region. The cognitive impairment caused by LPS injection could be reversed by blocking GABA receptor activity with (−)-Bicuculline methiodide. These findings suggest that the upregulation of GABAergic synapses induced by LPS-mediated microglial activation leads to cognitive dysfunction. Additionally, the depletion of microglia by PLX3397 resulted in a decrease in GABAergic interneurons and GABAergic inhibitory synapses, which blocked the cognitive decline induced by LPS. In conclusion, our findings indicate that excessive reinforcement of GABAergic inhibitory synapse formation via microglial activation contributes to LPS-induced cognitive impairment.

ADAM17 aggravates the inflammatory response by modulating microglia polarization through the TGF-β1/Smad pathway following experimental traumatic brain injury.

Microglia-mediated neuroinflammatory responses play important roles in secondary neurological injury after traumatic brain injury (TBI). The TGF-β pathway participates in the regulation of M1/M2 phenotype transformation of microglia. TGF-β can activate the Smad pathway by binding to TGF-βRs, which is regulated by the cleavage function of A disintegrin and metalloproteinase 17 (ADAM17). However, the role of ADAM17 and the associated signaling pathways in the pathological process after TBI remain unclear. Herein, we assessed the transformation of microglia M1/M2 phenotype polarization and the neuroinflammatory response after the inhibition of ADAM17. The formation of TGF-βRs and TGF-β1/TGF-βRII complexes on microglia were detected to evaluate the effect of ADAM17 inhibition on the TGF-β1/Smad pathway. ADAM17 was highly expressed after TBI and mainly located in the microglia. the inhibition of ADAM17 improved neurological function after TBI. The neuroprotective effect of ADAM17 inhibition was related to a shift from the M1 microglial phenotype to the M2 microglial phenotype, thus reducing TBI-induced neuroinflammation. ADAM17 inhibition increased expression of TGF-βRs on the microglia membrane, promoted formation of TGF-β1/TGF-βRII complexes, and induced intranuclear translocation of Smads, which activated the TGF-β/Smad pathway. In conclusion, our study suggested that ADAM17 inhibition regulated microglia M1/M2 phenotype polarization through the TGF-β1/Smad pathway and influenced the neuroinflammatory response after TBI.

Three-dimensional-cultured MSC-derived exosome with hydrogel for cerebral ischemia repair

Microglia-mediated neuroinflammatory response, one of the most essential pathological processes of cerebral ischemia-reperfusion (I/R) injury, is acknowledged as the main factors leading to poor prognosis of cerebral ischemia. Exosome derived from mesenchymal stem cell (MSC-Exo) exhibits neuroprotective functions by reducing cerebral ischemia-induced neuroinflammatory response and promoting angiogenesis. However, MSC-Exo has disadvantages such as insufficient targeting capability and low production, which limits their clinical applications. Here, we fabricated gelatin methacryloyl (GelMA) hydrogel for three-dimensional (3D) culture of MSCs. It is indicated that 3D environment could simulate the biological niches of MSCs, thereby significantly increasing the cell stemness of MSCs and improving the yield of MSCs-derived exosomes (3D-Exo). In this study, we utilized the modified Longa method to induce middle cerebral artery occlusion (MCAO) model. Additionally, in vitro and in vivo studies were conducted to interrogate the mechanism of the stronger neuroprotective effect of 3D-Exo. Furthermore, the administration of 3D-Exo in MCAO model could promote neovascularization in infarct region and result in a significant suppression of inflammatory response. This study proposed an exosome-based targeting delivery system for cerebral ischemia and provided a promising strategy for efficient and large-scale production of MSC-Exo.

The role of TREM1 in regulating microglial polarization in sevoflurane-induced perioperative neurocognitive disorders

Microglia-mediated neuroinflammatory responses play a key role in perioperative neurocognitive disorders (PND). Triggering receptor expressed on myeloid cells-1 (TREM1) has been shown to be a key regulator of inflammation. However, its role in PND remains largely unknown. This study aimed to evaluate the role of TREM1 in sevoflurane-induced PND. We applied AAV knockdown TREM1 in hippocampal microglia in aging mice. The mice were then subjected to neurobehavioral and biochemical testing after the intervention of sevoflurane. We found that sevoflurane inhalation can cause PND in mice, increase hippocampal TREM1 expression, polarize microglia to M1 type, upregulate TNF-α and IL-1β expression (pro-inflammatory), and inhibit TGF-β and IL-10 expression (anti-inflammatory). Knocking down TREM1 can improve sevoflurane-induced cognitive dysfunction, reduce M1 type marker iNOS, and increase M2 type marker ARG, improving the neuroinflammation. TREM1 is a target for sevoflurane-induced PND prevention.

Quercus acuta Thunb. Suppresses LPS-Induced Neuroinflammation in BV2 Microglial Cells via Regulating MAPK/NF-κB and Nrf2/HO-1 Pathway.

Microglial activation-mediated neuroinflammation is associated with the pathogenesis of neurodegenerative disorders. Therefore, the management of microglial cell activation and their inflammatory response is an important therapeutic approach for preventing neurodegenerative diseases. Quercus acuta Thunb. (QA) (Fagaceae) is a tree found in Korea, China, and Japan. The current study investigated the anti-neuroinflammatory effects of QA and its mechanism of action in lipopolysaccharide (LPS)-stimulated BV2 microglial cells. Pretreatment with a methanol extract of dried QA stems (QAE) inhibited the production of nitric oxide and proinflammatory cytokines and decreased the expression of inducible nitric oxide synthase, cyclooxygenase-2 in LPS-stimulated BV2 microglial cells. Furthermore, it inhibited the phosphorylation and degradation of inhibitory κBα and decreased the nuclear translocation and phosphorylation of nuclear factor-κB (NF-κB). Moreover, QAE inhibited the phosphorylation of extracellular signal-regulated kinase, p38 and c-Jun N-terminal kinase, which is known as mitogen-activated protein kinase (MAPK). Additionally, QAE treatment increased heme oxygenase-1 (HO-1) expression by activating the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling, thereby ameliorating LPS-induced intracellular hydrogen peroxide production. Finally, it was found that catechin and taxifolin, two phytochemicals of QAE, also reduced the expression of inflammatory mediators. These findings suggest that QA is beneficial for preventing microglia-mediated neuroinflammatory response through the inhibition of NF-κB, MAPK and the activation of Nrf2/HO-1 signaling pathways.

ACT001 attenuates microglia-mediated neuroinflammation after traumatic brain injury via inhibiting AKT/NF\u03baB/NLRP3 pathway

BackgroundMicroglia-mediated neuroinflammatory response following traumatic brain injury (TBI) is considered as a vital secondary injury factor, which drives trauma-induced neurodegeneration and is lack of efficient treatment. ACT001, a sesquiterpene lactone derivative, is reportedly involved in alleviation of inflammatory response. However, little is known regarding its function in regulating innate immune response of central nervous system (CNS) after TBI. This study aimed to investigate the role and underlying mechanism of ACT001 in TBI.MethodsControlled cortical impact (CCI) models were used to establish model of TBI. Cresyl violet staining, evans blue extravasation, neurobehavioral function assessments, immunofluorescence and transmission electron microscopy were used to evaluate therapeutic effects of ACT001 in vivo. Microglial depletion was induced by administering mice with colony stimulating factor 1 receptor (CSF1R) inhibitor, PLX5622. Cell-cell interaction models were established as co-culture system to simulate TBI conditions in vitro. Cytotoxic effect of ACT001 on cell viability was assessed by cell counting kit-8 and activation of microglia cells were induced by Lipopolysaccharides (LPS). Pro-inflammatory cytokines expression was determined by Real-time PCR and nitric oxide production. Apoptotic cells were detected by TUNEL and flow cytometry assays. Tube formation was performed to evaluate cellular angiogenic ability. ELISA and western blot experiments were used to determine proteins expression. Pull-down assay was used to analyze proteins that bound ACT001.ResultsACT001 relieved the extent of blood-brain barrier integrity damage and alleviated motor function deficits after TBI via reducing trauma-induced activation of microglia cells. Delayed depletion of microglia with PLX5622 hindered therapeutic effect of ACT001. Furthermore, ACT001 alleviated LPS-induced activation in mouse and rat primary microglia cells. Besides, ACT001 was effective in suppressing LPS-induced pro-inflammatory cytokines production in BV2 cells, resulting in reduction of neuronal apoptosis in HT22 cells and improvement of tube formation in bEnd.3 cells. Mechanism by which ACT001 functioned was related to AKT/NFκB/NLRP3 pathway. ACT001 restrained NFκB nuclear translocation in microglia cells through inhibiting AKT phosphorylation, resulting in decrease of NLRP3 inflammasome activation, and finally down-regulated microglial neuroinflammatory response.ConclusionsOur study indicated that ACT001 played critical role in microglia-mediated neuroinflammatory response and might be a novel potential chemotherapeutic drug for TBI.FQdKbSYTeaAq3ny7ETc-jcVideo

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.

Nilotinib inhibits microglia-mediated neuroinflammation to protect against dopaminergic neuronal death in Parkinson’s disease models

Microglia-mediated neuroinflammation is tightly correlated with the etiology and progression of neurodegenerative disorders, including Parkinson’s disease (PD). Nilotinib, a c-Abl inhibitor used for chronic myeloid leukemia, has been proven effective in relieving PD progression. However, whether nilotinib could affect neuroinflammation is largely unknown. In this current study, we investigated the role of nilotinib in microglia-mediated neuroinflammatory response in Parkinson’s disease. Lipopolysaccharide (LPS)-induced neuroinflammation in BV2 microglial cells and mouse brains were used as models for Parkinson’s disease. Our results demonstrated that nilotinib significantly suppressed LPS-induced neuroinflammation by reducing the production of pro-inflammatory factors including iNOS, COX-2, IL-1β, IL-6 and TNF-α in BV2 cells. Moreover, pretreatment of nilotinib attenuated the neurotoxicity of LPS-treated microglial conditioned medium to MES23.5 dopaminergic (DA) neurons. Mechanismly, nilotinib inhibited NF-κB signaling pathway and suppressed the nuclear translocation of p65 upon LPS stimulation. In LPS-injected mouse brains, nilotinib administration markedly suppressed the activation of microglia and down-regulated COX-2 as well as IL-1β expression. Most importantly, nilotinib effectively protected against microglial activation-mediated mouse DA neuronal loss. Taken together, our study suggests that nilotinib exerts anti-neuroinflammatory effect and protects DA neurons from activated microglia-induced inflammatory damage through suppressing NF-κB signaling pathway, indicating its potential application in further clinical trials.

Transcriptome Analysis of Microglia Reveals That the TLR2/IRF7 Signaling Axis Mediates Neuroinflammation After Subarachnoid Hemorrhage.

Microglia-mediated neuroinflammatory response in the early brain injury after subarachnoid hemorrhage (SAH) has been reported to have an impact on progress, and the mechanism is not completely understood. Here, we performed genome-wide transcriptome analysis of microglia purified from damaged hemisphere of adult mice at 3 days after SAH or sham operation. Robust transcriptional changes were observed between SAH-induced and healthy microglia, indicating rapid activation of microglia after suffering from SAH. We identified 1576 differentially expressed genes (DEGs; 928 upregulated and 648 downregulated) in SAH-induced microglia compared with sham microglia, representing a strong alteration of the genome (6.85% of total ∼23,000 genes). Functional enrichment of these DEGs indicated that cell division, inflammatory response, cytokine production, and leukocyte chemotaxis were strongly activated in SAH-induced microglia. Moreover, we identified and proved that the TLR2/IRF7 signaling axis was involved in the regulation of this microglia-mediated inflammation in SAH mice by performing flow cytometry and immunofluorescence. Together, these results provided a perspective of microglia-mediated neuroinflammatory response in the early stage of SAH and might give a new therapeutic target for SAH.

Diphenyl diselenide protects motor neurons through inhibition of microglia-mediated inflammatory injury in amyotrophic lateral sclerosis

Microglia-mediated neuroinflammatory response and neuron damage are considered as a self-propelling progressive cycle, being strongly implicated in the progression of neurodegeneration in amyotrophic lateral sclerosis (ALS). Diphenyl diselenide (DPDS), a simple organoselenium compound, has been known to possess multiple pharmacological properties. The purpose of this study was to explore the neuroprotective effects of DPDS against microglia-mediated neuroinflammatory injury in ALS models. We found that DPDS pretreatment inhibited LPS-induced activation of IκB/NF-κB pathway and subsequent release of proinflammatory factors from activated primary hSOD1G93A microglia. Moreover, DPDS suppressed NLRP3 inflammasome activation by decreasing protein nitration via reduction in NO and ROS levels, whose low levels are related to NF-κB inhibition responsible for iNOS and NOX2 down-regulations, respectively. Notably, DPDS-mediated ROS attenuation was not linked to Nrf2 activation in this cellular model. Furthermore, in the absence of activated microglia, DPDS has no significant effect on the individual hSOD1G93A-NSC34 cells; however, in in vitro neuron-microglia conditional culture and co-culture experiments, DPDS protected motor neurons from neurotoxic damage caused by LPS or BzATP-stimulated microglia activation. Above observations suggest that DPDS-afforded neuroprotection is linked to inhibition of microglia-mediated neuroinflammation in ALS, which was further verified in vivo as shown by improvements of motor deficits, prolonged survival, and reduction of motor neuron loss and reactive microgliosis in hSOD1G93A transgenic mouse. Altogether, our results show that DPDS elicited neuroprotection in ALS models through inactivation of microglia by inhibiting IκB/NF-κB pathway and NLRP3 inflammasome activation, suggesting that DPDS may be a promising candidate for potential therapy for ALS.

The antidepressant effects of asperosaponin VI are mediated by the suppression of microglial activation and reduction of TLR4/NF-κB-induced IDO expression.

Indoleamine 2,3-dioxygenase 1 (IDO) is responsible for the progression of the kynurenine pathway, which has been implicated in the pathophysiology of inflammation-induced depression. It has been reported that asperosaponin VI (ASA VI) could play a neuroprotective role through anti-inflammatory and antioxidant. In this study, we examined the antidepressant effect of ASA VI in lipopolysaccharide (LPS)-treated mice and further explored its molecular mechanism by looking into the microglial kynurenine pathway. To generate the model, LPS (0.83mg/kg) was administered intraperitoneally to mice. The mice received ASA VI (10mg/kg, 20mg/kg, 40mg/kg, and 80mg/kg, i.p.) 30min before LPS injection. Depressive-like behaviors were evaluated based on the duration of immobility in the forced swim test. Microglial activation and inflammatory cytokines were detected by immunohistochemistry, real-time PCR, and ELISA. The TLR4/NF-κB signaling pathway and the expression of IDO, GluA2, and CamKIIβ were also measured by western blotting. ASA VI exhibited significant antidepressant activity in the presence of LPS on immobility and latency times in the forced swim test. The LPS-induced activation of microglia and inflammatory response were inhibited by ASA VI, which showed a dose-dependent pattern. TLR4/NF-κB signaling pathway also was suppressed by ASA VI in the hippocampus and prefrontal cortex of LPS-treated mice. Furthermore, ASA VI inhibited the increase in IDO protein expression and normalized the aberrant glutamate transmission in the hippocampus and prefrontal cortex caused by LPS administration. Our results propose a promising antidepressant effect for ASA VI possibly through the downregulation of IDO expression and normalization of the aberrant glutamate transmission. This remedying effect of ASA VI could be attributed to suppress microglia-mediated neuroinflammatory response via inhibiting the TLR4/NF-κB signaling pathway.

A Multifunctional Chemical Agent as an Attenuator of Amyloid Burden and Neuroinflammation in Alzheimer's Disease.

Alzheimer's disease (AD) is the most common neurodegenerative disease, and its main hallmark is the deposition of amyloid beta (Aβ) peptides. However, several clinical trials focusing on Aβ-targeting agents have failed recently, and thus new therapeutic leads are focusing on alternate targets such as tau protein pathology, Aβ-metal induced oxidative stress, and neuroinflammation. To address these different pathological aspects of AD, we have employed a multifunctional compound, L1 [4-(benzo[d]thiazol-2-yl)-2-((4,7-dimethyl-1,4,7-triazonan-1-yl)methyl)-6-methoxyphenol], that integrates Aβ-interacting and metal-binding fragments in a single molecular framework, exhibits significant antioxidant activity and metal chelating ability, and also rescues neuroblastoma N2A cells from Cu2+-induced Aβ neurotoxicity. Along with demonstrating in vivo Aβ-binding and favorable brain uptake properties, L1 treatment of transgenic 5xFAD mice significantly reduces the amount of both amyloid plaques and associated phosphorylated tau (p-tau) aggregates in the brain by 40-50% versus the vehicle-treated 5xFAD mice. Moreover, L1 mitigates the neuroinflammatory response of the activated microglia during the Aβ-induced inflammation process. Overall, these multifunctional properties of L1 to attenuate the formation of amyloid plaques and associated p-tau aggregates while also reducing the microglia-mediated neuroinflammatory response are quite uncommon among the previously reported amyloid-targeting chemical agents, and thus L1 could be envisioned as a lead compound for the development of novel AD therapeutics.

Neuroprotection provided by Omega-3 polyunsaturated fatty acid through inhibiting microglia-mediated neuroinflammatory response in cognitive impairment rats

Objective To investigate the effects and mechanisms of Omega-3 polyunsaturated fatty acid (ω-3 PUFA) supplementation on spatial learning and memory capacity, neuronal apoptosis, microglia activation, neuroinflammatory response and nuclear factor-κB (NF-κB) pathway in cognitive impairment model rats. Methods Cognitive impairment model rats were induced by intraperitoneal injection of D-galactose. Thirty-six Wistar rats were randomly divided into three groups: control group (Con), Cognitive impairment group (AD) and ω-3 PUFA supplementation group (AD+ ω-3). The spatial learning and memory capacity of experimental rats were examined by the Morris water maze (MWM). Apoptotic neurons were determined by Nissl staining. The microglia activation relatived protein (Iba-1) expressions was determined by immunohistochemistry staining and western blot, respectively. While, the serum levels of tumor necrosis factor-α(TNF-α), interleukin (IL)-1 and IL-6 were tested by enzyme linked immunosorbent assay (ELISA). In addition, the protein expression of NF-κB related indexes including NF-κB p65, p-IκB and TLR4 were tested using western blot. Results Compared with the Con group, the escape latency increased and the distance percentage in target quadrant decreased; neurons apoptosis, microglia activation and neuroinflammatory factors significantly increased in the other two groups(P=0.00). Compared with the AD group, the escape latency was remarkably shorter(2 d: 41.35±2.34 vs. 58.07±3.27, P=0.03; 3 d: 35.07±2.45 vs. 44.39±3.21, P=0.02; 4d: 28.12±2.43 vs. 35.63±2.20, P=0.01; 5 d: 23.74±1.06 vs. 29.76±1.15, P=0.03), and the distance percentage in target quadrant increased significantly [(48.26±4.02)% vs.(34.14±3.49)%, P=0.01] after ω-3 PUFA supplementation. The incidence of neurons apoptosis significantly decreased in AD+ ω-3 group [(29.93 ±3.05)% vs.(47.58±4.14)%, P=0.01]. ω-3 PUFA supplementation inhibited the protein expression of microglia, and meanwhile inhibed the expression of microglia-induced neuroinflammatory factors [TNF-α: (85.27±9.77 vs. 156.13±14.53)pg/ml, P=0.00; IL-1: (41.23±5.38 vs. 75.04±9.27)pg/ml, P=0.01; IL-6: (47.58±4.23 vs. 97.47±9.09)pg/ml, P=0.00]. Compared with AD group, the protein expression of NF-κB pathway significantly decreased in AD+ ω-3 group. Conclusion ω-3 PUFA supplementation can inhibited microglia activation, decrease microglia-mediated neuroinflammatory response, reduce neuron apoptosis and markedly improve spatial learning and memory capacity in cognitive impairment rats, possibly mediated by inhibiting NF-κB pathway. Key words: Alzheimer′s disease; Cognitive impairment; Omega-3 polyunsaturated fatty acid; Microglia; Inflammatory response; NF-κB pathway

Water-Soluble Arginyl-Diosgenin Analog Attenuates Hippocampal Neurogenesis Impairment Through Blocking Microglial Activation Underlying NF-κB and JNK MAPK Signaling in Adult Mice Challenged by LPS.

Microglia-mediated neuroinflammatory responses are well known to inhibit neurogenesis in the dentate gyrus (DG) of the adult hippocampus, and growing evidence indicates that therapeutic intervention to suppress microglial activation could be an effective strategy for restoring the impaired neurogenesis and memory performance. In the present study, we investigated the effects of water-soluble arginyl-diosgenin analog (Arg-DG) on the adult hippocampal neurogenesis using a central LPS-induced inflammatory mice model, along with the fundamental mechanisms in vivo and in vitro using LPS-stimulated microglial BV2 cells. Arg-DG (0.6mg/kg) attenuates LPS-impaired neurogenesis by ameliorating the proliferation and differentiation of neural stem cells (NSCs), and prolonging their survival. The impaired neurogenesis in the hippocampal DG triggered the cognitive function, and that treatment of Arg-DG led to the recovery of cognitive decline. Arg-DG also suppressed the production of LPS-induced pro-inflammatory cytokines in hippocampal DG by blocking microglial activation. In in vitro study, Arg-DG inhibited the production of nitric oxide (NO), nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) expression, and prostaglandin D2 production (PGD2), as well as the pro-inflammatory cytokines, such as interleukin (IL)-6, IL-1β, and tumor necrosis factor alpha (TNF-α). The anti-inflammatory effect of Arg-DG was regulated by NF-κB and MAPK JNK signaling both in vivo, and in LPS-stimulated microglial BV2 cells. Taken together, these results suggest that Arg-DG might have the potential to treat various neurodegenerative disorders resulting from microglia-mediated neuroinflammation.

Glutamine supplementation provides neuroprotection by inhibiting microglia-mediated neuroinflammatory response after traumatic brain injury in rats

Objective To investigate the effects and mechanisms of Glutamine(Gln) supplementation on neurobehavioral outcome, neuronal apoptosis, microglia polarization, and neuroinflammatory response after traumatic brain injury (TBI) in rats. Methods TBI animal models were established using Feeney's method. Sixty Wistar rats were randomly divided into three groups: control group (Con), traumatic brain injury group (TBI), and glutamine supplementation group (TBI+ Gln). We measured rat behavioral outcomes by modified neurologic severity score (mNSS) tests at day 1, 3, 7 and 14 after TBI. Apoptotic neurons were determined by Nissl staining. The microglia polarization relatived protein (Iba-1, CD16, CD86) expressions in TBI cerebral cortices were determined by immunohistochemistry staining and western blotting, respectively. While, the serum levels of tumor necrosis factor-α(TNF-α), interleukin (IL)-1 and interferon (IFN)-γ were tested by enzyme linked immunosorbent Assay (ELISA). Results Compared with the Con group, the levels of neurobehavioral outcome, neurons apoptosis, microglia polarization and neuroinflammatory factors were significantly increased in the other two groups(P=0.00). Compared with the TBl group, glutamin supplementation improved neurobehavioral outcome[7 d: (10.74±0.25)points vs. (8.94±0.24) points, P=0.01; 14 d: (8.77±0.16)points vs. (7.43±0.13)points, P=0.03]. Meanwhile, glutamin supplementation suppressed the apoptotic rates of neurons [3 d: (80.18±8.38)% vs.(65.47±7.02)%, P=0.01; 7 d: (58.90±6.12)% vs.(42.73±4.88)%, P=0.01; 14 d: (39.56±2.95)% vs.(31.12±3.16)%, P=0.01], inhibited protein expressions of Iba-1 and CD16, and increased the protein expression of CD86, which promoted the phenotypic shift of microglia from M1 to M2 phenotype, inhibited microglial activation, and thus reduced TBI-induced neuroinflammatory factors [TNF-α: (125.42±12.81)pg/ml vs. (74.36±9.25)pg/ml, P=0.01; IL-1: (69.04±8.48)pg/ml vs. (34.73±3.92)pg/ml, P=0.01; TNF-α: (89.75±9.40)pg/ml vs. (45.62±6.64)pg/ml, P=0.02]. Conclusion Glutamine supplementation can markedly reduce neuron apoptosis and improve neurological outcomes after TBI, possibly mediated by promoting the phenotypic shift of microglia from M1 to M2 phenotype and thus reducing TBI-induced neuroinflammatory factors. Key words: Traumatic brain injury; Glutamine; Microglia; Inflammatory response; Neuroprotection

BHDPC Is a Novel Neuroprotectant That Provides Anti-neuroinflammatory and Neuroprotective Effects by Inactivating NF-κB and Activating PKA/CREB.

Microglia-mediated neuroinflammatory responses are inevitable and important pathological processes in several kinds of disorder of the central nervous system (CNS). Therefore, alleviating activated microglia-induced inflammatory process might be a valuable therapeutic approach to neuroinflammation-related diseases. In the present study, we investigated BHDPC, a novel neuroprotectant discovered in our previous study that had anti-inflammatory effects under neuroinflammatory conditions. First, we found that BHDPC could inhibit neuroinflammatory responses and promote microglial M2 phenotype polarization in both lipopolysaccharide (LPS)-activated BV-2 microglia l cells. Furthermore, BHDPC provided protective actions against neuroinflammation-induced neurotoxicity in HT22 mouse hippocampal cells co-cultured with activated BV-2 microglia. Further experiments demonstrated that BHDPC could suppress LPS-induced activation of transcription factor nuclear factor kappa B (NF-κB) via interfering with the degradation of the inhibitor of kappa B (IκB) and phosphorylation of IκB, the IκB kinase (IKK). Moreover, we also found that BHDPC could induce phosphorylation of cAMP-dependent protein kinase A (PKA) and cAMP-response element-binding protein (CREB) in BV-2 microglial cells. Also, using the PKA-specific inhibitor, we found that BHDPC-induced CREB phosphorylation was dependent on PKA, which also contributed to BHDPC-mediated anti-inflammation and neuroprotection.

Valproic Acid Attenuates Traumatic Brain Injury-Induced Inflammation in Vivo: Involvement of Autophagy and the Nrf2/ARE Signaling Pathway.

Microglial activation and the inflammatory response in the central nervous system (CNS) play important roles in secondary damage after traumatic brain injury (TBI). Transcriptional activation of genes that limit secondary damage to the CNS are mediated by a cis-acting element called the antioxidant responsive element (ARE). ARE is known to associate with the transcription factor NF-E2-related factor 2 (Nrf2), a transcription factor that is associated with histone deacetylases (HDACs). This pathway, known as the Nrf2/ARE pathway, is a critical antioxidative factor pathway that regulates the balance of oxygen free radicals and the inflammatory response, and is also related to autophagic activities. Although valproic acid (VPA) is known to inhibit HDACs, it is unclear whether VPA plays a role in the microglia-mediated neuroinflammatory response after TBI via regulating oxidative stress and autophagy induced by the Nrf2/ARE signaling pathway. In this study, we demonstrate that microglial activation, oxidative stress, autophagy, and the Nrf2/ARE signaling pathway play essential roles in secondary injury following TBI. Treatment with VPA alleviated TBI-induced secondary brain injury, including neurological deficits, cerebral edema, and neuronal apoptosis. Moreover, VPA treatment upregulated the occurrence of autophagy and Nrf2/ARE pathway activity after TBI, and there was an increase in H3, H4 histone acetylation levels, accompanied by decreased transcriptional activity of the HDAC3 promoter in cortical lesions. These results suggest that VPA-mediated up-regulation of autophagy and antioxidative responses are likely due to increased activation of Nrf2/ARE pathway, through direct inhibition of HDAC3. This inhibition further reduces TBI-induced microglial activation and the subsequent inflammatory response, ultimately leading to neuroprotection.

Impaired IL-17 Production in Gut-Residing Immune Cells of 5xFAD Mice with Alzheimer's Disease Pathology.

Alzheimer's disease (AD) is characterized by accumulation of amyloid-β plaques that further promotes microglia-mediated neuroinflammatory responses and inflammation in the brain. Emerging data are revealing the relation between gut-associated lymphoid tissue (GALT) cells and CNS, as effector cells primed in the gut might home to the brain. This study aimed to determine cell composition of GALT in 5xFAD mice, an established model for AD. Immune cells isolated from Peyer's patches (PP) and mesenteric lymph nodes (MLN) were stained with surface and intracellular markers for T helper (Th) subpopulations, B lymphocytes and macrophages and analyzed cytofluorimetrically, while cytokine expression and production were determined by qPCR and ELISA, respectively. Inflammation was detected in GALT of 5xFAD mice with established AD pathology. Although the production of IFN-γ, IL-4, and IL-10 was comparable between the strains, lower IL-17 production was observed in PP and MLN cells. This phenomenon could not be attributed to a lower abundance of Th17 cells, or cytokines that initiate their formation or propagation (TGF-β, IL-6, and IL-23). Also, reduced IL-17 production was not a consequence of altered Il-17 mRNA transcription or deficiency of Rorγt, a key transcription factor for IL-17. However, the expression of miR-155 (a non-coding micro RNA that promotes the development of Th17 cells), was significantly lower in MLN cells of 5xFAD mice. In contrast, mice without AD neuropathology did not have inflammation in GALT or altered Th17 numbers, nor decreased IL-17 production. In conclusion, the observed changes in GALT of 5xFAD mice mirror the disease progression and might reflect inadequate immune surveillance in the gut and lead to enhanced AD pathology.

Inhibition of cathepsin L alleviates the microglia-mediated neuroinflammatory responses through caspase-8 and NF-κB pathways

Cathepsin L (CTSL) has been shown to participate in the microglia-mediated neuroinflammation. However, the role of CTSL in neuroinflammation remains to be elucidated. In this study, CTSL was found to be upregulated on lipopolysaccharide (LPS) stimulation. The neuroinflammatory responses on LPS stimulation were ameliorated by inhibition or deficiency of CTSL in vitro or vivo. Treatment with conditioned medium of activated BV2 cells in SH-SY5Y cells showed that CTSL inhibition reduced microglia-mediated neurotoxicity. Further analysis indicated that CTSL was involved in the activation of caspase-8 and NF-κB, and overexpression of CTSL-enhanced expression of inflammatory mediators in response to LPS via caspase-8 and NF-κB pathways. Moreover, mRNA level of CTSL in peripheral blood mononuclear cells from patients with Parkinson's disease was higher compared with controls. Level of CTSL was positively correlated with expression of inflammatory mediators and NF-κB in Parkinson's disease patients. Taken together, these findings suggested that inhibition of CTSL alleviated the neuroinflammatory responses through caspase-8 and NF-κB pathways, and blocking CTSL might provide some clues to control the excessive neuroinflammation.