Progesterone therapy induces an M1 to M2 switch in microglia phenotype and suppresses NLRP3 inflammasome in a cuprizone-induced demyelination mouse model

Microglial NLRP3 inflammasome activation in multiple sclerosis

Multiple sclerosis (MS) is a chronic, autoimmune and neuroinflammatory disease of the central nervous system (CNS) mediated by autoreactive T cells directed against myelin antigens. Although the crucial role of adaptive immunity is well established in MS, the contribution of innate immunity has only recently been appreciated. Microglia are the main innate immune cells of the CNS. Similar to other myeloid cells, microglia recognize both exogenous and host-derived endogenous danger signals through pattern recognition receptors (PRRs) localized on their cell surface such as Toll Like receptor 4, or in the cytosol such as NLRP3. The second one is the sensor protein of the multi-molecular NLRP3 inflammasome complex in activated microglia that promotes the maturation and secretion of proinflammatory cytokines, interleukin-1β and interleukin-18. Overactivation of microglia and aberrant activation of the NLRP3 inflammasome have been implicated in the pathogenesis of MS. Indeed, experimental data, together with post-mortem and clinical studies have revealed an increased expression of NLRP3 inflammasome complex elements in microglia and other immune cells. In this review, we focus on microglial NLRP3 inflammasome activation in MS. First, we overview the basic knowledge about MS, microglia and the NLRP3 inflammasome. Then, we summarize studies about microglial NLRP3 inflammasome activation in MS and its animal models. We also highlight experimental therapeutic approaches that target different steps of NLRP inflammasome activation. Finally, we discuss future research avenues and new methods in this rapidly evolving area.

Intranasal delivery of SDF-1α-preconditioned bone marrow mesenchymal cells improves remyelination in the cuprizone-induced mouse model of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory and demyelinating disease of the central nervous system (CNS) that leads to disability in middle-aged individuals. High rates of apoptosis and inappropriate homing are limitations for the application of stem cells in cell therapy. Preconditioning of bone marrow mesenchymal stem cells (BMSCs) with stromal cell-derived factor 1α (SDF-1α), also called C-X-C motif chemokine 12 (CXCL12), is an approach for improving the functional features of the cells. The aim of this study was to investigate the therapeutic efficacy of intranasal delivery of SDF-1α preconditioned BMSCs in the cuprizone-induced chronically demyelinated mice model. BMSCs were isolated, cultured, and preconditioned with SDF-1α. Then, intranasal delivery of the preconditioned cells was performed in the C57BL/6 mice receiving cuprizone for 12 weeks. Animals were killed at 30 days after cell delivery. SDF-1α preconditioning increased C-X-C chemokine receptor type 4 (CXCR4) expression on the surface of BMSCs, improved survival of the cells, and decreased their apoptosis in vitro. SDF-1α preconditioning also improved CXCL12 level within the brain, and enhanced spatial learning and memory (assessed by Morris water maze [MWM]), and myelination (assessed by Luxol fast blue [LFB] and transmission electron microscopy [TEM]). In addition, preconditioning of BMSCs with SDF-1α reduced the protein expressions of glial fibrillary acidic protein and ionized calcium-binding adapter molecule (Iba-1) and increased the expressions of oligodendrocyte lineage transcription factor-2 (Olig-2) and adenomatous polyposis coli (APC), evaluated by immunofluorescence. The results showed the efficacy of intranasal delivery of SDF-1α-preconditioned BMSCs for improving remyelination in the cuprizone model of MS.

Neurosteroids as regulators of neuroinflammation

Neuroinflammation is a physiological protective response in the context of infection and injury. However, neuroinflammation, especially if chronic, may also drive neurodegeneration. Neurodegenerative diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD) and traumatic brain injury (TBI), display inflammatory activation of microglia and astrocytes. Intriguingly, the central nervous system (CNS) is a highly steroidogenic environment synthesizing steroids de novo, as well as metabolizing steroids deriving from the circulation. Neurosteroid synthesis can be substantially affected by neuroinflammation, while, in turn, several steroids, such as 17β-estradiol, dehydroepiandrosterone (DHEA) and allopregnanolone, can regulate neuroinflammatory responses. Here, we review the role of neurosteroids in neuroinflammation in the context of MS, AD, PD and TBI and describe underlying molecular mechanisms. Moreover, we introduce the concept that synthetic neurosteroid analogues could be potentially utilized for the treatment of neurodegenerative diseases in the future.

Behavioural phenotypes in the cuprizone model of central nervous system demyelination

The feeding of cuprizone (CPZ) to animals has been extensively used to model the processes of demyelination and remyelination, with many papers adopting a narrative linked to demyelinating conditions like multiple sclerosis (MS), the aetiology of which is unknown. However, no current animal model faithfully replicates the myriad of symptoms seen in the clinical condition of MS. CPZ ingestion causes mitochondrial and endoplasmic reticulum stress and subsequent apoptosis of oligodendrocytes leads to central nervous system demyelination and glial cell activation. Although there are a wide variety of behavioural tests available for characterizing the functional deficits in animal models of disease, including that of CPZ-induced deficits, they have focused on a narrow subset of outcomes such as motor performance, cognition, and anxiety. The literature has not been systematically reviewed in relation to these or other symptoms associated with clinical MS. This paper reviews these tests and makes recommendations as to which are the most important in order to better understand the role of this model in examining aspects of demyelinating diseases like MS.

A Benzenediamine Analog FC-99 Drives M2 Macrophage Polarization and Alleviates Lipopolysaccharide- (LPS-) Induced Liver Injury

Macrophages have variable functional phenotypes, high diversity, and plasticity and are involved in the pathogenesis of sepsis-induced liver injury. Alteration of macrophage polarization through activated (M1) macrophage to alternatively activated (M2) macrophage has emerged as a potential therapeutic strategy. This study was designed to explore the effect of a benzenediamine analog FC-99 on macrophage polarization in vitro and lipopolysaccharide- (LPS-) induced liver injury followed by the underlying mechanisms. For in vitro experiments, FC-99 inhibited M1-related macrophage factors and promoted M2-related markers induced by IL-4 in the mouse macrophage cell line RAW264.7. Moreover, FC-99-induced macrophages polarized to M2 phenotype which could be repressed by a PPAR-γ inhibitor but not STAT6 siRNA knockdown, indicating FC-99-induced M2 macrophage polarization through PPAR-γ rather than STAT6 signal. In LPS-induced septic mice, FC-99 pretreated mice displayed lower expression of M1 markers together with the increased M2 marker CD206 and improvement of liver injury. These findings illustrated that FC-99 could promote M2 macrophage polarization via PPAR-γ signaling and seemed to be a potential therapeutic candidate for inflammatory liver injury.

Effect of Fasudil on remyelination following cuprizone-induced demyelination

Background

Multiple sclerosis is characterized by demyelination/remyelination, neuroinflammation, and neurodegeneration. Cuprizone (CPZ)‐induced toxic demyelination is an experimental animal model commonly used to study demyelination and remyelination in the central nervous system. Fasudil is one of the most thoroughly studied Rho kinase inhibitors.

Methods

Following CPZ exposure, the degree of demyelination in the brain of male C57BL/6 mice was assessed by Luxol fast blue, Black Gold II, myelin basic protein immunofluorescent staining, and Western blot. The effect of Fasudil on behavioral change was determined using elevated plus maze test and pole test. The possible mechanisms of Fasudil action were examined by immunohistochemistry, flow cytometry, ELISA, and dot blot.

Results

Fasudil improved behavioral abnormalities, inhibited microglia‐mediated neuroinflammation, and promoted astrocyte‐derived nerve growth factor and ciliary neurotrophic factor, which should contribute to protection and regeneration of oligodendrocytes. In addition, Fasudil inhibited the production of myelin oligodendrocyte glycoprotein antibody and the infiltration of peripheral CD4⁺ T cells and CD68⁺ macrophages, which appears to be related to the integrity of the blood‐brain barrier.

Conclusion

These results provide evidence for the therapeutic potential of Fasudil in CPZ‐induced demyelination. However, how Fasudil acts on microglia, astrocytes, and immune cells remains to be further explored.

Astrocyte ablation induced by La-aminoadipate (L-AAA) potentiates remyelination in a cuprizone demyelinating mouse model

Chronic demyelination in the central nervous system (CNS) is accompanied by an increase in the number of reactive astrocytes and astrogliosis. There are controversial issues regarding astrocytes and their roles in demyelinating diseases in particular for multiple sclerosis (MS). We aimed to evaluate possible roles for pharmacologic astrocyte ablation strategy using La-aminoadipate (L-AAA) on remyelination in a cuprizone model of demyelination. Male C57BL/6 mice were fed with 0.2% cuprizone for 12 weeks followed by 2-week administration of L-AAA through a cannula inserted 1 mm above the corpus callosum. Rotarod test showed a significant decrease in the range of motor coordination deficits after ablation of astrocytes in mice receiving cuprizone. Results of Luxol fast blue (LFB) and transmission electron microscopy (TEM) for evaluation of myelin content within the corpus callosum revealed a noticeable rise in the percentage of myelinated areas and in the number of myelinated fibers after L-AAA administration in the animals. Astrocyte ablation reduced protein expressions for GFAP (an astrocyte marker) and Iba-1 (a microglial marker), but increased expression of Olig2 (an oligodendrocyte marker) assessed by immunofluorescence. Finally, expression of genes related to recruitment of microglia (astrocyte chemokines CXCL10 and CXCL12) and suppression of oligodendrocyte progenitor cell (OPC) differentiation (astrocyte peptides ET-1 and EDNRB) showed a considerable decrease after administration of L-AAA (for all p < 0.05). These results are indicative of improved remyelination after ablation of astrocytes possibly through hampering microgliosis and astrogliosis and a further rise in the number of matured Olig2+ cells.

Melatonin in macrophage biology: Current understanding and future perspectives

Melatonin is a ubiquitous hormone found in various organisms and highly affects the function of immune cells. In this review, we summarize the current understanding of the significance of melatonin in macrophage biology and the beneficial effects of melatonin in macrophage-associated diseases. Enzymes associated with synthesis of melatonin, as well as membrane receptors for melatonin, are found in macrophages. Indeed, melatonin influences the phenotype polarization of macrophages. Mechanistically, the roles of melatonin in macrophages are related to several cellular signaling pathways, such as NF-κB, STATs, and NLRP3/caspase-1. Notably, miRNAs (eg, miR-155/-34a/-23a), cellular metabolic pathways (eg, α-KG, HIF-1α, and ROS), and mitochondrial dynamics and mitophagy are also involved. Thus, melatonin modulates the development and progression of various macrophage-associated diseases, such as cancer and rheumatoid arthritis. This review provides a better understanding about the importance of melatonin in macrophage biology and macrophage-associated diseases.

Isoflurane preconditioning ameliorates electromagnetic pulse-induced neural damage by shifting microglia polarization toward anti-inflammatory phenotype via upregulation of SOCS1

With the speedy technological advances during the past few decades, human exposure to the electromagnetic field (EMF) has become increasingly common. Exposure to EMF may induce neural injuries and dysfunction of various organs, likely involving neuroinflammation and activation of microglial cells. Isoflurane preconditioning (IP) is shown to provide neuroprotection in various neurological diseases by inhibiting excessive neuroinflammatory responses. Brain samples harvested from rats exposed to electromagnetic pulse (EMP) with or without IP were subjected to qPCR, Western blot assay, and immunohistochemistry to determine the expression of pro-inflammatory/anti-inflammatory microglia markers and a variety of pro- and anti-inflammatory mediators. Suppressor of cytokine signaling 1 (SOCS1) siRNA was used in cultured N9 microglia cells to examine the roles of SOCS1 in the effect of IP. In both in vivo and in vitro experiments, EMP-exposed microglia were predominantly pro-inflammatory microglia, accompanied by increased expression of pro-inflammatory cytokines and chemokines, and activation of TLR4 pathway, leading to neuronal death. IP reversed the changes induced by EMP and switched the activated microglia to an anti-inflammatory phenotype. SOCS1 siRNA abolished the beneficial effects of IP. IP ameliorates EMP-induced neural injuries by shifting microglia polarization from pro-inflammatory to anti-inflammatory phenotype via upregulation of SOCS1.

Progesterone effects on the oligodendrocyte linage: all roads lead to the progesterone receptor

A new role has emerged for progesterone after discovering its potent actions away from reproduction in both the central and the peripheral nervous system. The aim of the present report is to discuss progesterone’s mechanisms of action involved in myelination, remyelination and neuroinflammation. The pivotal role of the classic progesterone receptor is described and evidence is compiled about progesterone’s direct effects on oligodendrocyte linage and its indirect effects on oligodendrocyte precursor cell differentiation by decreasing the neuroinflammatory environment.

Progesterone effects on oligodendrocyte differentiation in injured spinal cord

Spinal cord lesions result in chronic demyelination as a consequence of secondary injury. Although oligodendrocyte precursor cells proliferate the differentiation program fails. Successful differentiation implies progressive decrease of transcriptional inhibitors followed by upregulation of activators. Progesterone emerges as an anti-inflammatory and pro-myelinating agent which improves locomotor outcome after spinal cord injury. In this study, we have demonstrated that spinal cord injury enhanced oligodendrocyte precursor cell number and decreased mRNA expression of transcriptional inhibitors (Id2, Id4, hes5). However, mRNA expression of transcriptional activators (Olig2, Nkx2.2, Sox10 and Mash1) was down-regulated 3 days post injury. Interestingly, a differentiation factor such as progesterone increased transcriptional activator mRNA levels and the density of Olig2- expressing oligodendrocyte precursor cells. The differentiation program is regulated by extracellular signals which modify transcriptional factors and epigenetic players. As TGFβ1 is a known oligodendrocyte differentiation factor which is regulated by progesterone in reproductive tissues, we assessed whether TGFβ1 could mediate progesterone remyelinating actions after the lesion. Notwithstanding that astrocyte, oligodendrocyte precursor and microglial cell density increased after spinal cord injury, the number of these cells which expressed TGFβ1 remained unchanged regarding sham operated rats. However, progesterone treatment increased TGFβ1 mRNA expression and the number of astrocytes and microglial TGFβ1 expressing cells which would indirectly enhance oligodendrocyte differentiation. Therefore, TGFβ1 arises as a potential mediator of progesterone differentiating effects on oligodendrocyte linage.

Tuftsin Combines With Remyelinating Therapy and Improves Outcomes in Models of CNS Demyelinating Disease

Though promoting remyelination in multiple sclerosis (MS) has emerged as a promising therapeutic strategy, it does not address inflammatory signals that continue to induce neuronal damage and inhibit effectiveness of repair mechanisms. Our lab has previously characterized the immunomodulatory tetrapeptide, tuftsin, which induces an anti-inflammatory shift in microglia and macrophages. This targeted anti-inflammatory agent improves physical deficits in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Here, we sought to determine whether tuftsin is also effective in combination with benztropine, an FDA-approved drug that stimulates remyelination, in both EAE and in the cuprizone model of demyelination. We show that combining these two agents to promote anti-inflammatory and remyelinating mechanisms alleviates symptoms in EAE and lessens pathological hallmarks in both MS models. Importantly, tuftsin is required to transform the inflammatory CNS environment normally present in EAE/MS into one of an anti-inflammatory nature, and benztropine is required in the cuprizone model to improve remyelination. Our data further support tuftsin's beneficial immunomodulatory activity in the context of EAE, and show that when studying remyelination in the absence of an autoimmune insult, tuftsin still activated microglia toward an anti-inflammatory fate, but benztropine was necessary for significant repair of the damaged myelin. Overall, tuftsin effectively combined with benztropine to significantly improve MS-like pathologies in both models.

Changes in neurosteroidogenesis during demyelination and remyelination in cuprizone-treated mice

Changes of neurosteroids may be involved in the pathophysiology of multiple sclerosis (MS). The present study investigated whether changes of neurosteroidogenesis also occurred in the grey and white matter regions of the brain in mice subjected to cuprizone-induced demyelination. Accordingly, we compared the expression of neurosteroidogenic proteins, including steroidogenic acute regulatory protein (StAR), voltage-dependent anion channel (VDAC) and 18 kDa translocator protein (TSPO), as well as neurosteroidogenic enzymes, including the side chain cleavage enzyme (P450scc), 3β-hydroxysteroid dehydrogenase/isomerase and 5α-reductase (5α-R), during the demyelination and remyelination periods. Using immunohistochemistry and a quantitative polymerase chain reaction, we demonstrated a decreased expression of StAR, P450scc and 5α-R with respect to an increase astrocytic and microglial reaction and elevated levels of tumor necrosis factor (TNF)α during the cuprizone demyelination period in the hippocampus, cortex and corpus callosum. These parameters, as well as the glial reaction, were normalised after 2 weeks of spontaneous remyelination in regions containing grey matter. Conversely, persistent elevated levels of TNFα and low levels of StAR and P450scc were observed during remyelination in corpus callosum white matter. We conclude that neurosteroidogenesis/myelination status and glial reactivity are inversely related in the hippocampus and neocortex. Establishing a cause and effect relationship for the measured variables remains a future challenge for understanding the pathophysiology of MS.

Microglia polarization by methylprednizolone acetate accelerates cuprizone induced demyelination

Glucocorticoids (GC) are known as inflammatory drugs, which are used in neuroinflammatory diseases. Unlike the classic picture, recent studies have revealed that some GC drugs exacerbate inflammatory responses in their acute and prolonged administration. Multiple sclerosis (MS) is a demyelinating inflammatory disorder, in which reactive M1 microglia phenotype play a central role. Since methylprednisolone (MP), as a synthetic GC, are commonly used by MS patients, in this study, we evaluated the effect of long-term administration of MP on microglia polarization in cuprizone (CPZ)-induced MS model. The immunostaining results showed that chronic exposure to MP in the CPZ treated mice increased the number of Iba-1 positive microglia, which significantly expressed IP10 as M1 marker than arginase as M2 marker. MP treatment induced significant amplification in the transcript levels of iNOS and TNF-α (M1-related markers) in the corpus callosum of the MS mice, whereas no change detected in the expression of IL-10 (M2-related marker) between the groups. In addition, evaluation of myelin by luxol fast blue staining and transmission electron microscopy revealed that prolonged MP administration increased demyelination in comparison to the CPZ group. In conclusion, our results show that chronic MP therapy in the CPZ-induced demyelination model of MS polarized microglia to M1 pro-inflammatory phenotype.

Crocin, a natural product attenuates lipopolysaccharide-induced anxiety and depressive-like behaviors through suppressing NF-kB and NLRP3 signaling pathway

Depression is one of the foremost psychological illness which is closely leagued with inflammation. Crocin is a natural product that exhibits both anti-inflammatory and anti-oxidant activities. However, little is known about anti-inflammatory mechanisms of crocin on LPS-induced anxiety and depressive-like behaviors. The objective of this study is emphasized on neuroprotective role of crocin against LPS-induced anxiety and depressive-like behaviors in mice. It is observed that crocin inhibited LPS-induced production of NO, TNF-α, IL-1β and ROS in BV-2 microglial cells. Moreover, crocin significantly declined the expression of iNOS, NF-κB p65 and CD16/32 (M1 marker), as well as elevated the expression of CD206 (M2 marker) in BV-2 cell line with decreased LPS-induced anxiety and depressive-like behaviors by improved locomotor activity, reduced sucrose intake, and decreased immobility time in forced swim and tail suspension test in Kunming mice. Expression of NLRP3, ASC and caspase-1 by i.p administration of LPS found to be neutralized with reduction in level of IL-1β, IL-18 and TNF-α in mouse hippocampus. In conclusion, these results suggested that crocin as a potential therapeutic candidate for neuro-inflammation and depressive-like behaviors induced by LPS. The effect was found to be due to inhibition of NLRP3 inflammasome and NF-κB and its promoted M1 to M2 phenotypic conversion of microglia.

Chemopreventive Effects of Phytochemicals and Medicines on M1/M2 Polarized Macrophage Role in Inflammation-Related Diseases

Macrophages can polarize into two different states (M1 and M2), which play contrasting roles during pathogenesis or tissue damage. M1 polarized macrophages produce pro-inflammatory cytokines and mediators resulting in inflammation, while M2 macrophages have an anti-inflammatory effect. Secretion of appropriate cytokines and chemokines from macrophages can lead to the modification of the microenvironment for bridging innate and adaptive immune responses. Increasing evidence suggests that polarized macrophages are pivotal for disease progression, and the regulation of macrophage polarization may provide a new approach in therapeutic treatment of inflammation-related diseases, including cancer, obesity and metabolic diseases, fibrosis in organs, brain damage and neuron injuries, and colorectal disease. Polarized macrophages affect the microenvironment by secreting cytokines and chemokines while cytokines or mediators that are produced by resident cells or tissues may also influence macrophages behavior. The interplay of macrophages and other cells can affect disease progression, and therefore, understanding the activation of macrophages and the interaction between polarized macrophages and disease progression is imperative prior to taking therapeutic or preventive actions. Manipulation of macrophages can be an entry point for disease improvement, but the mechanism and potential must be understood. In this review, some advanced studies regarding the role of macrophages in different diseases, potential mechanisms involved, and intervention of drugs or phytochemicals, which are effective on macrophage polarization, will be discussed.

Targeting the NLRP3 Inflammasome-Related Pathways via Tianeptine Treatment-Suppressed Microglia Polarization to the M1 Phenotype in Lipopolysaccharide-Stimulated Cultures

An increasing body of evidence postulates that microglia are the main mediators of inflammation-related disorders, including depression. Since activated microglia produce a wide range of pro- and anti-inflammatory factors, the modulation of M1/M2 microglial polarization by antidepressants may be crucial in the treatment of depression. The current paper aimed to investigate the impact of tianeptine on the microglia’s viability/death parameters, and on M1/M2 microglial activation in response to lipopolysaccharide (LPS) stimulation. Furthermore, the molecular mechanisms via which tianeptine affected the LPS-evoked changes were investigated. The results revealed that tianeptine had partially protective effects on the changes in microglia viability/death evoked by LPS. Tianeptine attenuated microglia activation by decreasing the expression of cluster of differentiation 40 (CD40), and major histocompatibility complex class II (MHC II) markers, as well as the release of pro-inflammatory factors: interleukin (IL)-1β, IL-18, IL-6, tumor necrosis factor alpha (TNF-α), and chemokine CC motif ligand 2 (CCL2), and the production of nitric oxide and reactive oxygen species. In contrast, we did not observe an impact of tianeptine on M2 microglia measured by IL-4, IL-10, TGF-β, and insulin-like growth factor 1 (IGF-1) expression. Moreover, we demonstrated an inhibitory effect of tianeptine on the LPS-induced activation of the nucleotide-binding oligomerization domain-like (NOD-like) receptor pyrin-containing 3 inflammasome (NLRP3) inflammasome subunits, NLRP3 and caspase-1, as well as the ability of tianeptine to reduce Toll-like receptor 4 (TLR4) levels, as well as the phosphorylation of extracellular signal-related kinases 1 and 2 (ERK1/2) and of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Collectively, we demonstrated that tianeptine has protective properties and inhibits M1 polarization, thus attenuating the production of inflammatory mediators. Moreover, we found that M1 microglia suppression may be related to the NLRP3 inflammasome and TLR4 signaling. These findings suggest that a better understanding of the multifaceted mechanisms of tianeptine action on microglia may increase the effectiveness of therapy, where inflammation is a central hallmark.

Omega-3 polyunsaturated fatty acid attenuates the inflammatory response by modulating microglia polarization through SIRT1-mediated deacetylation of the HMGB1/NF-κB pathway following experimental traumatic brain injury

Background

Microglial polarization and the subsequent neuroinflammatory response are contributing factors for traumatic brain injury (TBI)-induced secondary injury. High mobile group box 1 (HMGB1) mediates the activation of the NF-κB pathway, and it is considered to be pivotal in the late neuroinflammatory response. Activation of the HMGB1/NF-κB pathway is closely related to HMGB1 acetylation, which is regulated by the sirtuin (SIRT) family of proteins. Omega-3 polyunsaturated fatty acids (ω-3 PUFA) are known to have antioxidative and anti-inflammatory effects. We previously demonstrated that ω-3 PUFA inhibited TBI-induced microglial activation and the subsequent neuroinflammatory response by regulating the HMGB1/NF-κB signaling pathway. However, no studies have elucidated if ω-3 PUFA affects the HMGB1/NF-κB pathway in a HMGB1 deacetylation of dependent SIRT1 manner, thus regulating microglial polarization and the subsequent neuroinflammatory response.

Methods

The Feeney DM TBI model was adopted to induce brain injury in rats. Modified neurological severity scores, rotarod test, brain water content, and Nissl staining were employed to determine the neuroprotective effects of ω-3 PUFA supplementation. Assessment of microglia polarization and pro-inflammatory markers, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and HMGB1, were used to evaluate the neuroinflammatory responses and the anti-inflammatory effects of ω-3 PUFA supplementation. Immunofluorescent staining and western blot analysis were used to detect HMGB1 nuclear translocation, secretion, and HMGB1/NF-κB signaling pathway activation to evaluate the effects of ω-3 PUFA supplementation. The impact of SIRT1 deacetylase activity on HMGB1 acetylation and the interaction between HMGB1 and SIRT1 were assessed to evaluate anti-inflammation effects of ω-3 PUFAs, and also, whether these effects were dependent on a SIRT1-HMGB1/NF-κB axis to gain further insight into the mechanisms underlying the development of the neuroinflammatory response after TBI.

Results

The results of our study showed that ω-3 PUFA supplementation promoted a shift from the M1 microglial phenotype to the M2 microglial phenotype and inhibited microglial activation, thus reducing TBI-induced inflammatory factors. In addition, ω-3 PUFA-mediated downregulation of HMGB1 acetylation and its extracellular secretion was found to be likely due to increased SIRT1 activity. We also found that treatment with ω-3 PUFA inhibited HMGB1 acetylation and induced direct interactions between SIRT1 and HMGB1 by elevating SIRT1 activity following TBI. These events lead to inhibition of HMGB1 nucleocytoplasmic translocation/extracellular secretion and alleviated HMGB1-mediated activation of the NF-κB pathway following TBI-induced microglial activation, thus inhibiting the subsequent inflammatory response.

Conclusions

The results of this study suggest that ω-3 PUFA supplementation attenuates the inflammatory response by modulating microglial polarization through SIRT1-mediated deacetylation of the HMGB1/NF-κB pathway, leading to neuroprotective effects following experimental traumatic brain injury.

Role of Inflammasomes in Neuroimmune and Neurodegenerative Diseases: A Systematic Review

Inflammasomes are multiprotein complexes that can sense pathogen-associated molecular patterns and damage-associated molecular signals. They are involved in the initiation and development of inflammation via activation of IL-1β and IL-18. Many recent studies suggest a strong correlation between inflammasomes and neurological diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), and Parkinson's disease (PD). Several components of inflammasomes, such as nucleotide-binding oligomerization domain- (NOD-) like receptor, absent in melanoma 2- (AIM2-) like receptors (ALRs), apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and caspase-1, as well as the upstream factors and downstream effectors, are associated with the initiation and development of MS and its animal model, experimental autoimmune encephalomyelitis. Additionally, inflammasomes affect the efficacy of interferon-β therapy in patients with MS. Finally, the strong association of inflammasomes with AD and PD needs to be further studied. In this review of latest literatures, we comprehensively tease out diverse roles of different kinds of inflammasomes in neuroimmune and neurodegenerative diseases, especially in the perspective of double roles involved in pathogenesis, and identify future research priorities.

The roles of macrophages and microglia in multiple sclerosis and experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an autoimmune and neurodegenerative disorder characterized by chronic inflammation, demyelination, as well as axonal and neuronal loss in the central nervous system (CNS). Macrophages and microglia are important components of the innate immune system. They participate in the primary response to microorganisms and play a role in inflammatory responses, homeostasis, and tissue regeneration. In the initial phase of MS and experimental autoimmune encephalomyelitis (EAE), an animal model of MS, macrophages from peripheral tissues infiltrate into the CNS and, together with residential microglia, contribute to the pathogenesis of MS. In the early stages, microglia and macrophages are expressed as the M1 phenotype, which can release proinflammatory cytokines, leading to tissue damage in the CNS. However, in the later stage, the M2 phenotype, which is the phenotype that is associated with resolving inflammation and tissue repair, becomes predominant in the CNS. Therefore, it is hypothesized that the M1/M2 phenotype balance plays an important role in disease progression and that the transition from the proinflammatory M1 phenotype to the regulatory or anti-inflammatory M2 phenotype can lead to restoration of homeostasis and improved functional outcomes. This review of recent literature focuses on the discussion of the M1/M2 phenotypes of microglia and macrophages as well as their relevance in the pathophysiology and treatment of MS and EAE. Furthermore, the possibility of directing the polarization of microglia and macrophages toward the M2 phenotype as a therapeutic and preventative strategy for MS is discussed.