Microglial activation and dopaminergic cell injury: an in vitro model relevant to Parkinson's disease

The humoral immune landscape in Parkinson's disease: Unraveling antibody and B cell changes

Parkinson's disease (PD) is a complex neurodegenerative disorder characterized by the accumulation of α-synuclein (α-syn) in the brain and progressive loss of dopaminergic neurons in the substantia nigra (SN) region of the brain. Although the role of neuroinflammation and cellular immunity in PD has been extensively studied, the involvement of humoral immunity mediated by antibodies and B cells has received less attention. This article provides a comprehensive review of the current understanding of humoral immunity in PD. Here, we discuss alterations in B cells in PD, including changes in their number and phenotype. Evidence mostly indicates a decrease in the quantity of B cells in PD, accompanied by a shift in the population from naïve to memory cells. Furthermore, the existence of autoantibodies that target several antigens in PD has been investigated (i.e., anti-α-syn autoantibodies, anti-glial-derived antigen antibodies, anti-Tau antibodies, antineuromelanin antibodies, and antibodies against the renin-angiotensin system). Several autoantibodies are generated in PD, which may either provide protection or have harmful effects on disease progression. Furthermore, we have reviewed studies focusing on the utilization of antibodies as a potential treatment for PD, both in animal and clinical trials. This review sheds light on the intricate interplay between antibodies and the pathological processes in PD, including complement system activation.

Alterations of mRNAs and Non-coding RNAs Associated with Neuroinflammation in Alzheimer's Disease

Alzheimer's disease is a neurodegenerative pathology whose pathognomonic hallmarks are increased generation of β-amyloid (Aβ) peptide, production of hyperphosphorylated (pTau), and neuroinflammation. The last is an alteration closely related to the progression of AD and although it is present in multiple neurodegenerative diseases, the pathophysiological events that characterize neuroinflammatory processes vary depending on the disease. In this article, we focus on mRNA and non-coding RNA alterations as part of the pathophysiological events characteristic of neuroinflammation in AD and the influence of these alterations on the course of the disease through interaction with multiple RNAs related to the generation of Aβ, pTau, and neuroinflammation itself.

Rethinking Parkinson's disease: could dopamine reduction therapy have clinical utility?

Following reports of low striatal dopamine content in Parkinson's disease, levodopa was shown to rapidly reverse hypokinesis, establishing the model of disease as one of dopamine deficiency. Dopaminergic therapy became standard of care, yet it failed to reverse the disease, suggesting the understanding of disease was incomplete. The literature suggests the potential for toxicity of dopamine and its metabolites, perhaps more relevant given the recent evidence for elevated cytosolic dopamine levels in the dopaminergic neurons of people with Parkinson's. To understand the relevance of these data, multiple investigations are reviewed that tested dopamine reduction therapy as an alternative to dopaminergic agents. The data from use of an inhibitor of dopamine synthesis in experimental models suggest that such an approach could reverse disease pathology, which suggests that cytosolic dopamine excess is a primary driver of disease. These data support clinical investigation of dopamine reduction therapy for Parkinson's disease. Doing so will determine whether these experimental models are predictive and this treatment strategy is worth pursuing further. If clinical data are positive, it could warrant reconsideration of our disease model and treatment strategies, including a shift from dopaminergic to dopamine reduction treatment of the disease.

Role of pyroptosis in the pathogenesis of various neurological diseases

Pyroptosis, an inflammatory programmed cell death process, has recently garnered significant attention due to its pivotal role in various neurological diseases. This review delves into the intricate molecular signaling pathways governing pyroptosis, encompassing both caspase-1 dependent and caspase-1 independent routes, while emphasizing the critical role played by the inflammasome machinery in initiating cell death. Notably, we explore the Nucleotide-binding domain leucine-rich repeat (NLR) containing protein family, the Absent in melanoma 2-like receptor family, and the Pyrin receptor family as essential activators of pyroptosis. Additionally, we comprehensively examine the Gasdermin family, renowned for their role as executioner proteins in pyroptosis. Central to our review is the interplay between pyroptosis and various central nervous system (CNS) cell types, including astrocytes, microglia, neurons, and the blood-brain barrier (BBB). Pyroptosis emerges as a significant factor in the pathophysiology of each cell type, highlighting its far-reaching impact on neurological diseases. This review also thoroughly addresses the involvement of pyroptosis in specific neurological conditions, such as HIV infection, drug abuse-mediated pathologies, Alzheimer's disease, and Parkinson's disease. These discussions illuminate the intricate connections between pyroptosis, chronic inflammation, and cell death in the development of these disorders. We also conducted a comparative analysis, contrasting pyroptosis with other cell death mechanisms, thereby shedding light on their unique aspects. This approach helps clarify the distinct contributions of pyroptosis to neuroinflammatory processes. In conclusion, this review offers a comprehensive exploration of the role of pyroptosis in various neurological diseases, emphasizing its multifaceted molecular mechanisms within various CNS cell types. By elucidating the link between pyroptosis and chronic inflammation in the context of neurodegenerative disorders and infections, it provides valuable insights into potential therapeutic targets for mitigating these conditions.

The role of microglia heterogeneity in synaptic plasticity and brain disorders: Will sequencing shed light on the discovery of new therapeutic targets?

Microglia play a crucial role in interacting with neuronal synapses and modulating synaptic plasticity. This function is particularly significant during postnatal development, as microglia are responsible for removing excessive synapses to prevent neurodevelopmental deficits. Dysregulation of microglial synaptic function has been well-documented in various pathological conditions, notably Alzheimer's disease and multiple sclerosis. The recent application of RNA sequencing has provided a powerful and unbiased means to decipher spatial and temporal microglial heterogeneity. By identifying microglia with varying gene expression profiles, researchers have defined multiple subgroups of microglia associated with specific pathological states, including disease-associated microglia, interferon-responsive microglia, proliferating microglia, and inflamed microglia in multiple sclerosis, among others. However, the functional roles of these distinct subgroups remain inadequately characterized. This review aims to refine our current understanding of the potential roles of heterogeneous microglia in regulating synaptic plasticity and their implications for various brain disorders, drawing from recent sequencing research and functional studies. This knowledge may aid in the identification of pathogenetic biomarkers and potential factors contributing to pathogenesis, shedding new light on the discovery of novel drug targets. The field of sequencing-based data mining is evolving toward a multi-omics approach. With advances in viral tools for precise microglial regulation and the development of brain organoid models, we are poised to elucidate the functional roles of microglial subgroups detected through sequencing analysis, ultimately identifying valuable therapeutic targets.

Current methods for the microglia isolation: Overview and comparative analysis of approaches

Microglia represent a distinct population of neuroglia, constituting ~ 10% of all CNS cells and exhibit high plasticity. Proper functioning of microglia is critical in the event of CNS damage due to the rapid modulation of their functions. Microglia are not only the first stage of immune defense against injury and infection, contributing to both the innate and adaptive local immune response, but also play a vital role in maintaining homeostasis of the brain and spinal cord. For this reason, microglia deserve special attention in the study of neuropathological responses. Studying microglia behavior in various in vivo models of neuropathologies is certainly a priority, as it allows us to evaluate the behavior in the context of the changing microenvironment of nervous tissue. However, sometimes there are some technological problems that hinder the identification of the features of intercellular interactions, ensured cooperation between microglia and other cell types. In this regard, the use of in vitro models remains relevant today, contributing to a more in-depth understanding of the mechanisms of microglial involvement in neuropathology. The methods considered in this review for obtaining an isolated culture of microglia, along with their advantages and disadvantages, can help researchers in selecting the appropriate source and method for obtaining these cells, thereby opening up opportunities for gaining new neurobiological knowledge.

Passive immunotherapy for Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease characterized by cognitive impairment with few therapeutic options. Despite many failures in developing AD treatment during the past 20 years, significant advances have been achieved in passive immunotherapy of AD very recently. Here, we review characteristics, clinical trial data, and mechanisms of action for monoclonal antibodies (mAbs) targeting key players in AD pathogenesis, including amyloid-β (Aβ), tau and neuroinflammation modulators. We emphasized the efficacy of lecanemab and donanemab on cognition and amyloid clearance in AD patients in phase III clinical trials and discussed factors that may contribute to the efficacy and side effects of anti-Aβ mAbs. In addition, we provided important information on mAbs targeting tau or inflammatory regulators in clinical trials, and indicated that mAbs against the mid-region of tau or pathogenic tau have therapeutic potential for AD. In conclusion, passive immunotherapy targeting key players in AD pathogenesis offers a promising strategy for effective AD treatment.

The Impact of Intestinal Microbiota and Toll-like Receptor 2 Signaling on α-Synuclein Pathology in Nontransgenic Mice Injected with α-Synuclein Preformed Fibrils

Intestinal microbiota and Toll-like receptor 2 (TLR2), which can bind lipoteichoic acid produced by microbiota, might contribute to the pathogenesis of Parkinson's disease (PD), which is characterized by α-synuclein accumulation. Although the contribution of intestinal microbiota and TLR2 to PD pathology was validated in genetic PD models, evidence suggests that the effects of TLR2 signaling on proteinopathy might depend on the presence of a genetic etiology. We examined the impact of intestinal microbiota and TLR2 signaling on α-synuclein pathology in a nontransgenic mouse model of sporadic PD. While an α-synuclein preformed fibrils injection successfully reproduced PD pathology by inducing accumulation of α-synuclein aggregates, microglial activation and increased TLR2 expression in the brains of nontransgenic mice, antibiotic-induced reduction in the density of intestinal microbiota and TLR2 knockout had small impact on these changes. These findings, which are in contrast to those reported in transgenic mice harboring transgene encoding α-synuclein, indicate that the contribution of intestinal microbiota and TLR2 signaling to α-synuclein pathogenesis might be influenced by the presence of a genetic etiology. Additionally, these findings suggest that integrating insights from this experimental model and genetic models would further advance our understanding of the molecular mechanisms underlying sporadic PD.

Epigenetic Regulation of Neuroinflammation in Alzheimer's Disease

Alzheimer's disease (AD) is a chronic and progressive neurodegenerative disease and clinically manifests with cognitive decline and behavioral disabilities. Over the past years, mounting studies have demonstrated that the inflammatory response plays a key role in the onset and development of AD, and neuroinflammation has been proposed as the third major pathological driving factor of AD, ranking after the two well-known core pathologies, amyloid β (Aβ) deposits and neurofibrillary tangles (NFTs). Epigenetic mechanisms, referring to heritable changes in gene expression independent of DNA sequence alterations, are crucial regulators of neuroinflammation which have emerged as potential therapeutic targets for AD. Upon regulation of transcriptional repression or activation, epigenetic modification profiles are closely involved in inflammatory gene expression and signaling pathways of neuronal differentiation and cognitive function in central nervous system disorders. In this review, we summarize the current knowledge about epigenetic control mechanisms with a focus on DNA and histone modifications involved in the regulation of inflammatory genes and signaling pathways in AD, and the inhibitors under clinical assessment are also discussed.

By-Product Extracts from Castanea sativa Counteract Hallmarks of Neuroinflammation in a Microglial Model

Castanea sativa is very common in Italy, and the large amount of waste material generated during chestnut processing has a high environmental impact. Several studies demonstrated that chestnut by-products are a good source of bioactive compounds, mainly endowed with antioxidant properties. This study further investigates the anti-neuroinflammatory effect of chestnut leaf and spiny bur extracts, together with the deepest phytochemical characterisation (by NMR and MS) of active biomolecules contained in leaf extracts, which resulted in being more effective than spiny bur ones. BV-2 microglial cells stimulated with lipopolysaccharide (LPS) were used as a model of neuroinflammation. In BV-2 cells pre-treated with chestnut extracts, LPS signalling is partially blocked via the reduced expression of TLR4 and CD14 as well as the expression of LPS-induced inflammatory markers. Leaf extract fractions revealed the presence of specific flavonoids, such as isorhamnetin glucoside, astragalin, myricitrin, kaempferol 3-rhamnosyl (1-6)(2″-trans-p-coumaroyl)hexoside, tiliroside and unsaturated fatty acids, all of which could be responsible for the observed anti-neuroinflammatory effects. Interestingly, the kaempferol derivative has been identified in chestnut for the first time. In conclusion, the exploitation of chestnut by-products is suitable for the achievement of two goals: satisfaction of consumers’ demand for new, natural bio-active compounds and valorisation of by-products.

Emerging roles of leptin in Parkinson's disease: Chronic inflammation, neuroprotection and more?

An increasing body of experimental evidence implicates a relationship between immunometabolic deterioration and the progression of Parkinson's disease (PD) with a dysregulation of central and peripheral neuroinflammatory networks mediated by circulating adipokines, in particular leptin. We screened the current literature on the role of adipokines in PD. Hence, we searched known databases (PubMed, MEDLINE/OVID) and reviewed original and review articles using the following terms: "leptin/ObR", "Parkinson's disease", "immune-metabolism", "biomarkers" and "neuroinflammation". Focusing on leptin, we summarize and discuss the existing in vivo and in vitro evidence on how adipokines may be protective against neurodegeneration, but at the same time contribute to the progression of PD. These components of the adipose brain axis represent a hitherto underestimated pathway to study systemic influences on dopaminergic degeneration. In addition, we give a comprehensive update on the potential of adjunctive therapeutics in PD targeting leptin, leptin-receptors, and associated pathways. Further experimental and clinical trials are needed to elucidate the mechanisms of action and the value of central and peripheral adipose-immune-metabolism molecular phenotyping in order to develop and validate the differential roles of different adipokines as potential therapeutic target for PD patients.

Increased levels of a pro-inflammatory IgG receptor in the midbrain of people with schizophrenia

BACKGROUND

There is growing evidence that neuroinflammation may contribute to schizophrenia neuropathology. Elevated pro-inflammatory cytokines are evident in the midbrain from schizophrenia subjects, findings that are driven by a subgroup of patients, characterised as a "high inflammation" biotype. Cytokines trigger the release of antibodies, of which immunoglobulin G (IgG) is the most common. The level and function of IgG is regulated by its transporter (FcGRT) and by pro-inflammatory IgG receptors (including FcGR3A) in balance with the anti-inflammatory IgG receptor FcGR2B. Testing whether abnormalities in IgG activity contribute to the neuroinflammatory abnormalities schizophrenia patients, particularly those with elevated cytokines, may help identify novel treatment targets.

METHODS

Post-mortem midbrain tissue from healthy controls and schizophrenia cases (n = 58 total) was used to determine the localisation and abundance of IgG and IgG transporters and receptors in the midbrain of healthy controls and schizophrenia patients. Protein levels of IgG and FcGRT were quantified using western blot, and gene transcript levels of FcGRT, FcGR3A and FcGR2B were assessed using qPCR. The distribution of IgG in the midbrain was assessed using immunohistochemistry and immunofluorescence. Results were compared between diagnostic (schizophrenia vs control) and inflammatory (high vs low inflammation) groups.

RESULTS

We found that IgG and FcGRT protein abundance (relative to β-actin) was unchanged in people with schizophrenia compared with controls irrespective of inflammatory subtype. In contrast, FcGRT and FcGR3A mRNA levels were elevated in the midbrain from "high inflammation" schizophrenia cases (FcGRT; p = 0.02, FcGR3A; p < 0.0001) in comparison to low-inflammation patients and healthy controls, while FcGR2B mRNA levels were unchanged. IgG immunoreactivity was evident in the midbrain, and approximately 24% of all individuals (control subjects and schizophrenia cases) showed diffusion of IgG from blood vessels into the brain. However, the intensity and distribution of IgG was comparable across schizophrenia cases and control subjects.

CONCLUSION

These findings suggest that an increase in the pro-inflammatory Fcγ receptor FcGR3A, rather than an overall increase in IgG levels, contribute to midbrain neuroinflammation in schizophrenia patients. However, more precise information about IgG-Fcγ receptor interactions is needed to determine their potential role in schizophrenia neuropathology.

Kaempferol exerts a neuroprotective effect to reduce neuropathic pain through TLR4/NF-ĸB signaling pathway

Switching microglial polarization from the M1 to M2 phenotype is a promising therapeutic strategy for neuropathic pain (NP). Toll‐like receptor 4 (TLR4) is activated by lipopolysaccharide (LPS). Uncontrolled activation of TLR4 has been proven to trigger chronic inflammation. Kaempferol, a dietary flavonoid, is known to have anti‐inflammatory properties. This study is aimed to investigate the analgesic and anti‐inflammatory effects and the underlying mechanisms of kaempferol, which were explored with an NP model in vivo and LPS‐induced injury in microglial BV2 cells in vitro. The levels of proinflammatory cytokines were evaluated. H&E staining and immunohistochemistry were used to assess the sciatic nerve condition after chronic constriction injury surgery. Western blotting and immunofluorescence were used to determine whether TLR4/NF‐ĸB signaling pathway plays a major role in kaempferol‐mediated alleviation of neuroinflammation. Quantitative real‐time polymerase chain reaction and flow cytometry were used to examine the modulator effect of kaempferol on microglial M1/M2 polarization. We found that kaempferol treatment can significantly reduce NP and proinflammatory cytokine production. Kaempferol attenuated the activation of TLR4/NF‐κB pathways in LPS‐activated BV2 cells. The analgesic effects of kaempferol on NP may be due to inhibition of microglia activation and switching the M1 to M2 phenotype.

Shaping the Microglia in Retinal Degenerative Diseases Using Stem Cell Therapy: Practice and Prospects

Retinal degenerative disease (RDD) refers to a group of diseases with retinal degeneration that cause vision loss and affect people's daily lives. Various therapies have been proposed, among which stem cell therapy (SCT) holds great promise for the treatment of RDDs. Microglia are immune cells in the retina that have two activation phenotypes, namely, pro-inflammatory M1 and anti-inflammatory M2 phenotypes. These cells play an important role in the pathological progression of RDDs, especially in terms of retinal inflammation. Recent studies have extensively investigated the therapeutic potential of stem cell therapy in treating RDDs, including the immunomodulatory effects targeting microglia. In this review, we substantially summarized the characteristics of RDDs and microglia, discussed the microglial changes and phenotypic transformation of M1 microglia to M2 microglia after SCT, and proposed future directions for SCT in treating RDDs.

Dopamine, a co-regulatory component, bridges the central nervous system and the immune system

Dopamine (DA) is a crucial neurotransmitter that plays an important role in maintaining physiological function in human body. In the past, most studies focused on the relationship between the dopaminergic system and neurological-related diseases. However, it has been found recently that DA is an immunomodulatory mediator and many immune cells express dopamine receptors (DRs). Some immune cells can synthesize and secrete DA and then participate in regulating immune function. DRs agonists or antagonists can improve the dysfunction of immune system through classical G protein signaling pathways or other non-receptor-dependent pathways. This article will discuss the relationship between the dopaminergic system and the immune system. It will also review the use of DRs agonists or antagonists to treat chronic and acute inflammatory diseases and corresponding immunomodulatory mechanisms.

Melittin administration ameliorates motor function, prevents apoptotic cell death and protects Purkinje neurons in the rat model of cerebellar ataxia induced by 3-Acetylpyridine

Cerebellar ataxia (CA) is a condition in which cerebellar dysfunction leads to movement disorders such as dysmetria, asynergy and dysdiadochokinesia. This study investigates the therapeutic effects of Melittin (MEL) on 3-acetylpyridine-induced (3-AP) cerebellar ataxia (CA) rat model. Initially, CA rat models were generated by 3-AP administration followed by the intraperitoneal injection of MEL. Then, motor performance and electromyography (EMG) activity were assessed. Afterwards, the pro-inflammatory cytokines were analyzed in the cerebellar tissue. Moreover, the anti-apoptotic role of MEL in CA and its relationship with the protection of Purkinje cells were explored. The findings showed that the administration of MEL in a 3-AP model of ataxia improved motor coordination (P < 0.001) and neuro-muscular activity (p < 0.05), prevented the cerebellar volume loss (P < 0.01), reduced the level of inflammatory cytokines (p < 0.05) and thwarted the degeneration of Purkinje cells against 3-AP toxicity (P < 0.001). Overall, the findings imply that the MEL attenuates the 3-AP-induced inflammatory response. As such, it could be used as a treatment option for CA due to its anti-inflammatory effects.

Parkinson Disease: Translating Insights from Molecular Mechanisms to Neuroprotection

Parkinson disease (PD) used to be considered a nongenetic condition. However, the identification of several autosomal dominant and recessive mutations linked to monogenic PD has changed this view. Clinically manifest PD is then thought to occur through a complex interplay between genetic mutations, many of which have incomplete penetrance, and environmental factors, both neuroprotective and increasing susceptibility, which variably interact to reach a threshold over which PD becomes clinically manifested. Functional studies of PD gene products have identified many cellular and molecular pathways, providing crucial insights into the nature and causes of PD. PD originates from multiple causes and a range of pathogenic processes at play, ultimately culminating in nigral dopaminergic loss and motor dysfunction. An in-depth understanding of these complex and possibly convergent pathways will pave the way for therapeutic approaches to alleviate the disease symptoms and neuroprotective strategies to prevent disease manifestations. This review is aimed at providing a comprehensive understanding of advances made in PD research based on leveraging genetic insights into the pathogenesis of PD. It further discusses novel perspectives to facilitate identification of critical molecular pathways that are central to neurodegeneration that hold the potential to develop neuroprotective and/or neurorestorative therapeutic strategies for PD. SIGNIFICANCE STATEMENT: A comprehensive review of PD pathophysiology is provided on the complex interplay of genetic and environmental factors and biologic processes that contribute to PD pathogenesis. This knowledge identifies new targets that could be leveraged into disease-modifying therapies to prevent or slow neurodegeneration in PD.

Role of Vitamin E and the Orexin System in Neuroprotection

Microglia are the first line of defense at the level of the central nervous system (CNS). Phenotypic change in microglia can be regulated by various factors, including the orexin system. Neuroinflammation is an inflammatory process mediated by cytokines, by the lack of interaction between neurotransmitters and their specific receptors, caused by systemic tissue damage or, more often, associated with direct damage to the CNS. Chronic activation of microglia could lead to long-term neurodegenerative diseases. This review aims to explore how tocopherol (vitamin E) and the orexin system may play a role in the prevention and treatment of microglia inflammation and, consequently, in neurodegenerative diseases thanks to its antioxidant properties. The results of animal and in vitro studies provide evidence to support the use of tocopherol for a reduction in microglia inflammation as well as a greater activation of the orexinergic system. Although there is much in vivo and in vitro evidence of vitamin E antioxidant and protective abilities, there are still conflicting results for its use as a treatment for neurodegenerative diseases that speculate that vitamin E, under certain conditions or genetic predispositions, can be pro-oxidant and harmful.

The Regulatory Role of Reticulons in Neurodegeneration: Insights Underpinning Therapeutic Potential for Neurodegenerative Diseases

In the last few decades, cytoplasmic organellar dysfunction, such as that of the endoplasmic reticulum (ER), has created a new area of research interest towards the development of serious health maladies including neurodegenerative diseases. In this context, the extensively dispersed family of ER-localized proteins, i.e. reticulons (RTNs), is gaining interest because of its regulative control over neural regeneration. As most neurodegenerative diseases are pathologically manifested with the accretion of misfolded proteins with subsequent induction of ER stress, the regulatory role of RTNs in neural dysfunction cannot be ignored. With the limited information available in the literature, delineation of the functional connection between rising consequences of neurodegenerative diseases and RTNs need to be elucidated. In this review, we provide a broad overview on the recently revealed regulatory roles of reticulons in the pathophysiology of several health maladies, with special emphasis on neurodegeneration. Additionally, we have also recapitulated the decisive role of RTN4 in neurite regeneration and highlighted how neurodegeneration and proteinopathies are mechanistically linked with each other through specific RTN paralogues. With the recent findings advocating zebrafish Rtn4b (a mammalian Nogo-A homologue) downregulation following central nervous system (CNS) lesion, RTNs provides new insight into the CNS regeneration. However, there are controversies with respect to the role of Rtn4b in zebrafish CNS regeneration. Given these controversies, the connection between the unique regenerative capabilities of zebrafish CNS by distinct compensatory mechanisms and Rtn4b signalling pathway could shed light on the development of new therapeutic strategies against serious neurodegenerative diseases.

Low dose gamma irradiation pretreatment modulates the sensitivity of CNS to subsequent mixed gamma and neutron irradiation of the mouse head

ABSTRACТPurpose: To explore if the total body γ-irradiation at a dose of 0.1 Gy 7 days prior to acute mixed γ, n-irradiation of the head at the dose of 1 Gy can reduce the harmful effects of neutron irradiation on the hippocampal functions, neuroinflammation and neurogenesis.Materials and methods: Mice were exposed to γ-radiation alone, mixed γ,n-radiation or combined γ-rays and γ,n-radiation 7 days after γ-irradiation. Two months post-irradiation, mice were tested in Open Field and in the Morris water maze. The content of microglia, astrocytes, proliferating cells and cytokines TGF-β, TNF-α, IL-1β, GFAP levels, hippocampal BDNF, NT-3, NT-4, NGF mRNA expression were evaluated.Results: Two months after combined irradiation, we observed impaired hippocampus-dependent cognition, which was not detected in mice exposed to γ,n-irradiation. Combined exposure and γ,n-irradiation led to a significant increase in the level of activated microglia and astrocytes in the brains. The level of pro- and anti-inflammatory cytokines in the brain and hippocampal neurotrophine's genes changed differenly after the combined exposure and γ,n-irradiation. The quantity of DCX-positive cells was reduced after γ,n-irradiation exposer alone, but increased after combined irradiation.Conclusions: Our results indicate radio-adaptive responses in brains of mice that were exposed to low-dose gamma irradiation 7 days prior to acute 1 Gy γ,n-irradiation.

Role of microgliosis, oxidative stress and associated neuroinflammation in the pathogenesis of Parkinson's disease: The therapeutic role of Nrf2 activators

Microglial cells are the resident immune cells of the central nervous system. They are essential for normal functioning, maintenance of tissue integrity, clearance of dying neurons, elimination of pathogens, development and maintenance of homeostasis of the CNS. Many studies have consistently reported that oxidative stress and associated neuroinflammation mediated by microglial cells have a degenerating effect on dopaminergic neurons. In Parkinson's disease, the microglial cells by a process called microgliosis undergo rapid proliferation, accumulate at the site of tissue injury and undergo phenotypic and functional changes that result in the release of massive amounts of free radicals causing inflammation and neurodegeneration of dopaminergic neurons. Following the discovery of the irrefutable role oxidative stress and associated neuroinflammation, several proven antioxidants were tested for possible protective and therapeutic potential in Parkinson's disease but the results so far have not been encouraging and equivocal. Consequently, it is rational to look for endogenous targets that enhance the oxidative defense mechanism against free radicals and protect dopaminergic neurons from neuroinflammation and neurodegeneration. One such target is a nuclear factor-erythroid -2-related factor 2 (Nrf2). Nrf2 is a redox-sensitive transcription factor located in the cytoplasm of the cells that helps cells adapt to oxidative stress and inflammation by upregulating the expression of almost 200 cytoprotective genes. Fractalkine exists in a transmembrane form and a soluble form and is a cytokine that links microglial cells and Nrf2. The fractalkine receptors, expressed exclusively by microglial cells, on activation by fractalkine protects dopaminergic neurons from degeneration caused by free radicals and pro-inflammatory mediators through increased expression of Nrf2 dependent genes. The current anti Parkinsonism drugs do not cure the disease and also cause several debilitating motor and non-motor adverse drug effects. So it becomes imperative to explore novel targets and discover novel therapeutic agents to treat Parkinson's disease in a better way and improve the quality of life of patients with Parkinson's disease.

Transcriptional profiling of microglia in the injured brain reveals distinct molecular features underlying neurodegeneration

Neurotrauma has been recognized as a risk factor for neurodegenerative diseases, and sex difference of the incidence and outcome of neurodegenerative diseases has long been recognized. Past studies suggest that microglia could play a versatile role in both health and disease. So far, the microglial mechanisms underlying neurodegeneration and potentially lead to sex-specific therapies are still very open. Here we applied whole transcriptome analysis of microglia acutely isolated at different timepoints after a cortical stab wound injury to gain insight into genes that might be dysregulated and transcriptionally different between males and females after cortical injury. We found that microglia displayed distinct temporal and sexual molecular signatures of transcriptome after cortical injury. Hypotheses and gene candidates that we presented in the present study could be worthy to be examined to explore the roles of microglia in neurotrauma and in sex-biased neurodegenerative diseases.

The Effects of Divalent Cation-Chelated Prion Fibrils on the Immune Response of EOC 13.31 Microglia Cells

Transmissible spongiform encephalopathies (TSEs) are epidemic neurodegenerative diseases caused by prion proteins; in particular, they are induced by misfolded prion proteins (PrPSc). PrPSc tend to aggregate into insoluble amyloid prion fibrils (fPrPWT), resulting in apoptosis of neuron cells and sequential neurodegeneration. Previous studies indicate that microglia cells play an important role in the innate immune system, and that these cells have good neuroprotection and delay the onset of TSEs. However, microglia can be a double-sided blade. For example, both Cu2+ and Mn2+ can induce microglia activation and secrete many inflammatory cytokines that are fatal to neuron cells. Unfortunately, PrP have cation binding sites at the N-terminus. When PrPSc accumulate during microglial phagocytosis, microglia may change the phenotype to secrete pro-inflammation cytokines, which increases the severity of the disease. Some studies have revealed an increase in the concentration of Mn2+ in the brains of patients. In this study, we treated microglia with fPrPWT and cations and determined IκBα and IL-1β expression by Western blotting and quantitative polymerase chain reaction. The results showed that Mn-fPrPWT decreased IκBα levels and dramatically increased IL-1β mRNA expression. In addition, competing binding between Cu2+ and Mn2+ can decrease the effect of Mn-fPrPWT on IκBα and IL-1β. The effects of divalent cations and fPrPWT in microglia inflammation are also discussed.

Overview of General and Discriminating Markers of Differential Microglia Phenotypes

Inflammatory processes and microglia activation accompany most of the pathophysiological diseases in the central nervous system. It is proven that glial pathology precedes and even drives the development of multiple neurodegenerative conditions. A growing number of studies point out the importance of microglia in brain development as well as in physiological functioning. These resident brain immune cells are divergent from the peripherally infiltrated macrophages, but their precise in situ discrimination is surprisingly difficult. Microglial heterogeneity in the brain is especially visible in their morphology and cell density in particular brain structures but also in the expression of cellular markers. This often determines their role in physiology or pathology of brain functioning. The species differences between rodent and human markers add complexity to the whole picture. Furthermore, due to activation, microglia show a broad spectrum of phenotypes ranging from the pro-inflammatory, potentially cytotoxic M1 to the anti-inflammatory, scavenging, and regenerative M2. A precise distinction of specific phenotypes is nowadays essential to study microglial functions and tissue state in such a quickly changing environment. Due to the overwhelming amount of data on multiple sets of markers that is available for such studies, the choice of appropriate markers is a scientific challenge. This review gathers, classifies, and describes known and recently discovered protein markers expressed by microglial cells in their different phenotypes. The presented microglia markers include qualitative and semi-quantitative, general and specific, surface and intracellular proteins, as well as secreted molecules. The information provided here creates a comprehensive and practical guide through the current knowledge and will facilitate the choosing of proper, more specific markers for detailed studies on microglia and neuroinflammatory mechanisms in various physiological as well as pathological conditions. Both basic research and clinical medicine need clearly described and validated molecular markers of microglia phenotype, which are essential in diagnostics, treatment, and prevention of diseases engaging glia activation.

Pharmacological Targeting of Microglial Activation: New Therapeutic Approach

Mounting evidence suggests that neuroinflammation is not just a consequence but a vital contributor to the development and progression of Parkinson’s disease (PD). Microglia in particular, may contribute to the induction and modulation of inflammation in PD. Upon stimulation, microglia convert into activated phenotypes, which exist along a dynamic continuum and bear different immune properties depending on the disease stage and severity. Activated microglia release various factors involved in neuroinflammation, such as cytokines, chemokines, growth factors, reactive oxygen species (ROS), reactive nitrogen species (RNS), and prostaglandins (PGs). Further, activated microglia interact with other cell types (e.g., neurons, astrocytes and mast cells) and are closely associated with α-synuclein (α-syn) pathophysiology and iron homeostasis disturbance. Taken together, microglial activation and microglia-mediated inflammatory responses play essential roles in the pathogenesis of PD and elucidation of the complexity and imbalance of microglial activation may shed light on novel therapeutic approaches for PD.

Apelin-36 mediates neuroprotective effects by regulating oxidative stress, autophagy and apoptosis in MPTP-induced Parkinson's disease model mice

Parkinson's disease (PD), a common human neurodegenerative disorder, is characterized by the presence of intraneuronal Lewy bodies composed principally of abnormal aggregated and post-translationally modified α-synuclein. In our previous research, we have demonstrated the neuroprotective effect of Apelin-36, a neuroendocrine peptide in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridin (MPTP)-lesioned PD model mice. Therefore, this study was designed to evaluate the neuroprotective mechanism of Apelin-36 against MPTP-induced neurotoxicity in mice. The results showed that MPTP-induced the depletion of dopamine in the striatum (STR) was partially reversed by Apelin-36. Apelin-36 also improved the activity of antioxidant system including superoxide dismutase (SOD) and glutathione (GSH), and decreased the overproduction of malondialdehyde (MDA) in the substantia nigra pars compacta (SNpc) and STR of MPTP-treated mice. Moreover, Apelin-36 downregulated inducible nitric oxide synthase (iNOS) and nitrated α-synuclein expression. Furthermore, Apelin-36 significantly promoted autophagy indicated by the up-regulation of LC3-II and Beclin1 and inhibition of p62 expression in the SNpc and STR of MPTP-treated mice. The protective effect of Apelin-36 was also associated with the inhibition of the apoptosis signal-regulating kinase 1 (ASK1)/c-Jun N-terminal kinase (JNK) signaling pathway and inactivation of caspase-3. Taken together, our findings demonstrated that the neuroprotective mechanism of Apelin-36 against MPTP-induced neurotoxicity in mice might be related to decreasing the aggregation of nitrated α-synuclein and alleviating oxidative stress as well as promoting autophagy and inhibiting ASK1/JNK/caspase-3 apoptotic pathway, which provides a novel strategy for PD treatment.

Aquaporin 4: A key player in Parkinson's disease

Parkinson's disease (PD) is one of the most prevalent neurodegenerative diseases which occur in aged people worldwide. Given that a sequence of cellular and molecular mechanisms, including oxidative stresses, apoptosis, inflammatory pathways, microglia, astrocyte activation, and aquaporin 4 (AQP4) are associated with initiation and the progression of PD. AQP4 may affect various pathways (i.e., α-synuclein, inflammatory pathways, and microglia and astrocyte activation). Few reports have evaluated the relationship between AQP4 and PD-related cellular and molecular pathways. Here, for the first time, we highlighted the relationship between AQP4 and molecular mechanisms involved in PD pathogenesis.

Promising Neuroprotective Function for M2 Microglia in Kainic Acid-Induced Neurotoxicity Via the Down-Regulation of NF-κB and Caspase 3 Signaling Pathways

Activated microglia have two functional states (M1 and M2) which play dual roles in neurodegenerative diseases. In the present study, we explored a possible neuroprotective function of M2 microglia against kainic acid (KA)-induced neurodegeneration in primary neurons co-cultured with different microglial populations. Neurons were isolated from the hippocampi and cortices of C57BL/6 embryos (embryonic day 16) and microglia were extracted from neonatal pups (postnatal days 0-2). Microglia were either unstimulated (M0-phenotype) or stimulated with lipopolysaccharide and interferon-γ to form the M1-phenotype, or with interleukin (IL)-4, IL-10, and transforming growth factor -β for the M2-phenotype. Neurons were co-cultured with each of the three microglial phenotypes and treated with KA for 24 h. Next, we analyzed the cell survival rate, nitric oxide (NO) levels, and lactate dehydrogenase production, cytokines levels, and expression of nuclear factor κB (NF-κB) and caspase 3 among the three groups before and after KA insult. Our results indicated that M2 microglia played a neuroprotective role in KA-induced neurotoxicity, as demonstrated by high neuronal survival as well as decreased production of NO and pro-inflammatory cytokines. In contrast, neurons co-cultured with M1 microglia exhibited the lowest survival rate as well as increased levels of NO and pro-inflammatory cytokines. Further, the expression of NF-κB and caspase 3 were significantly decreased in M2 microglia co-cultures compared to M1 or M0 microglia co-cultures after KA insult. Therefore, M2 microglia may exert a neuroprotective function in KA-induced neurotoxicity via the down-regulation of NF-κB and caspase 3 signaling pathways.

Physiological and Functional Basis of Dopamine Receptors and Their Role in Neurogenesis: Possible Implication for Parkinson's disease

Dopamine controls various physiological functions in the brain and periphery by acting on its receptors D1, D2, D3, D4, and D5. Dopamine receptors are G protein–coupled receptors involved in the regulation of motor activity and several neurological disorders such as schizophrenia, bipolar disorder, Parkinson’s disease (PD), Alzheimer’s disease, and attention-deficit/hyperactivity disorder. Reduction in dopamine content in the nigrostriatal pathway is associated with the development of PD, along with the degeneration of dopaminergic neurons in the substantia nigra region. Dopamine receptors directly regulate neurotransmission of other neurotransmitters, release of cyclic adenosine monophosphate, cell proliferation, and differentiation. Here, we provide an update on recent knowledge about the signalling mechanism, mode of action, and the evidence for the physiological and functional basis of dopamine receptors. We also highlight the pivotal role of these receptors in the modulation of neurogenesis, a possible therapeutic target that might help to slow down the process of neurodegeneration.

Gut, Microbiome, and Brain Regulatory Axis: Relevance to Neurodegenerative and Psychiatric Disorders

It has become apparent that the molecular and biochemical integrity of interactive families, genera, and species of human gut microflora is critically linked to maintaining complex metabolic and behavioral processes mediated by peripheral organ systems and central nervous system neuronal groupings. Relatively recent studies have established intrinsic ratios of enterotypes contained within the human microbiome across demographic subpopulations and have empirically linked significant alterations in the expression of bacterial enterotypes with the initiation and persistence of several major metabolic and psychiatric disorders. Accordingly, the goal of our review is to highlight potential thematic/functional linkages of pathophysiological alterations in gut microbiota and bidirectional gut-brain signaling pathways with special emphasis on the potential roles of gut dysbiosis on the pathophysiology of psychiatric illnesses. We provide critical discussion of putative thematic linkages of Parkinson's disease (PD) data sets to similar pathophysiological events as potential causative factors in the development and persistence of diverse psychiatric illnesses. Finally, we include a concise review of preclinical paradigms that involve immunologically-induced GI deficits and dysbiosis of maternal microflora that are functionally linked to impaired neurodevelopmental processes leading to affective behavioral syndromes in the offspring.

Urate inhibits microglia activation to protect neurons in an LPS-induced model of Parkinson's disease

Background

Multiple risk factors contribute to the progression of Parkinson’s disease, including oxidative stress and neuroinflammation. Epidemiological studies have revealed a link between higher urate level and a lower risk of developing PD. However, the mechanistic basis for this association remains unclear. Urate protects dopaminergic neurons from cell death induced by oxidative stress. Here, we investigated a novel role of urate in microglia activation in a lipopolysaccharide (LPS)-induced PD model.

Methods

We utilized Griess, ELISA, real-time PCR, Western blot, immunohistochemistry, and immunofluorescence to detect the neuroinflammation. For Griess, ELISA, Western blot, and immunofluorescence assay, cells were seeded in 6-well plates pre-coated with poly-l-lysine (PLL) and incubated for 24 h with the indicated drugs. For real-time PCR assay, cells were seeded in 6-well plates pre-coated with PLL and incubated for 6 h with the indicated drugs. For animal experiments, rats were injected with urate or its vehicle twice daily for five consecutive days before and after stereotaxic surgery. Rats were killed and brain tissues were harvested after 4 weeks of LPS injection.

Results

In cultured BV2 cells and rat primary microglia, urate suppressed proinflammatory cytokine production and inducible cyclooxygenase 2 and nitric oxide synthase expression to protect dopaminergic neurons from the toxic effects of activated microglia. The neuroprotective effects of urate may also be associated with the stimulation of anti-inflammatory factors interleukin 10 and transforming growth factor β1. Intracellular urate level was increased in a dose-dependent manner upon co-treatment with urate and LPS as compared with LPS alone, an effect that was abrogated by pretreatment with probenecid (PBN), an inhibitor of both glucose transporter 9 and urate transporter 1 (URAT1). PBN also abolished the anti-inflammatory effect of urate. Consistent with these in vitro observations, the number of tyrosine hydroxylase-positive neurons was decreased and the loss of motor coordination was reversed by urate administration in an LPS-induced rat model of PD. Additionally, increased plasma urate level abolished the reduction of URAT1 expression, the increase in the expression of interleukin-1β, and the number of ionized calcium-binding adaptor molecule 1-positive microglia along with changes in their morphology.

Conclusions

Urate protects neurons against cytotoxicity induced by microglia activation via modulating urate transporter-mediated intracellular urate level.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1175-8) contains supplementary material, which is available to authorized users.

Kir6.1/K-ATP channel modulates microglia phenotypes: implication in Parkinson's disease

Classical activation (M1 phenotype) and alternative activation (M2 phenotype) are the two polars of microglial activation states that can produce either neurotoxic or neuroprotective effects in the immune pathogenesis of Parkinson’s disease (PD). Exploiting the beneficial properties of microglia cells by modulating their polarization states provides great potential for the treatment of PD. However, the mechanism that regulates microglia polarization remains elusive. Here we demonstrated that Kir6.1-containing ATP-sensitive potassium (Kir6.1/K-ATP) channel switched microglia from the detrimental M1 phenotype toward the beneficial M2 phenotype. Kir6.1 knockdown inhibited M2 polarization and simultaneously exaggerated M1 microglial inflammatory responses, while Kir6.1 overexpression promoted M2 polarization and synchronously alleviated the toxic phase of M1 microglia polarization. Furthermore, we observed that the Kir6.1 deficiency dramatically exacerbated dopaminergic neuron death companied by microglia activation in mouse model of PD. Mechanistically, Kir6.1 deficiency enhanced the activation of p38 MAPK–NF-κB pathway and increased the ratio of M1/M2 markers in the substantia nigra compacta of mouse model of PD. Suppression of p38 MAPK in vivo partially rescued the deleterious effects of Kir6.1 ablation on microglia phenotype and dopaminergic neuron death. Collectively, our findings reveal that Kir6.1/K-ATP channel modulates microglia phenotypes transition via inhibition of p38 MAPK–NF-κB signaling pathway and Kir6.1/K-ATP channel may be a promising therapeutic target for PD.

Therapeutic Potential of Oridonin and Its Analogs: From Anticancer and Antiinflammation to Neuroprotection

Oridonin, a diterpenoid natural product commonly used in East Asian herbal medicine, is garnering increased attention in the biomedical community due to its extensive biological activities that include antitumor, anti-inflammatory, antimicrobial, hepatic fibrosis prevention, and neurological effects. Over the past decade, significant progress has been made in structure activity relationship and mechanism of action studies of oridonin for the treatment of cancer and other diseases. This review provides a brief summary on oridonin and its analogs in cancer drug discovery and antiinflammation and highlights its emerging therapeutic potential in neuroprotection applications.

In silico-based screen synergistic drug combinations from herb medicines: a case using Cistanche tubulosa

Neuroinflammation is characterized by the elaborated inflammatory response repertoire of central nervous system tissue. The limitations of the current treatments for neuroinflammation are well-known side effects in the clinical trials of monotherapy. Drug combination therapies are promising strategies to overcome the compensatory mechanisms and off-target effects. However, discovery of synergistic drug combinations from herb medicines is rare. Encouraged by the successfully applied cases we move on to investigate the effective drug combinations based on system pharmacology among compounds from Cistanche tubulosa (SCHENK) R. WIGHT. Firstly, 63 potential bioactive compounds, the related 133 direct and indirect targets are screened out by Drug-likeness evaluation combined with drug targeting process. Secondly, Compound-Target network is built to acquire the data set for predicting drug combinations. We list the top 10 drug combinations which are employed by the algorithm Probability Ensemble Approach (PEA), and Compound-Target-Pathway network is then constructed by the 12 compounds of the combinations, targets, and pathways to unearth the corresponding pharmacological actions. Finally, an integrating pathway approach is developed to elucidate the therapeutic effects of the herb in different pathological features-relevant biological processes. Overall, the method may provide a productive avenue for developing drug combination therapeutics.

The implication of neuronimmunoendocrine (NIE) modulatory network in the pathophysiologic process of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder implicitly marked by the substantia nigra dopaminergic neuron degeneration and explicitly characterized by the motor and non-motor symptom complexes. Apart from the nigrostriatal dopamine depletion, the immune and endocrine study findings are also frequently reported, which, in fact, have helped to broaden the symptom spectrum and better explain the pathogenesis and progression of PD. Nevertheless, based on the neural, immune, and endocrine findings presented above, it is still difficult to fully recapitulate the pathophysiologic process of PD. Therefore, here, in this review, we have proposed the neuroimmunoendocrine (NIE) modulatory network in PD, aiming to achieve a more comprehensive interpretation of the pathogenesis and progression of this disease. As a matter of fact, in addition to the classical motor symptoms, NIE modulatory network can also underlie the non-motor symptoms such as gastrointestinal, neuropsychiatric, circadian rhythm, and sleep disorders in PD. Moreover, the dopamine (DA)-melatonin imbalance in the retino-diencephalic/mesencephalic-pineal axis also provides an alternative explanation for the motor complications in the process of DA replacement therapy. In conclusion, the NIE network can be expected to deepen our understanding and facilitate the multi-dimensional management and therapy of PD in future clinical practice.

Protective effects of a green tea polyphenol, epigallocatechin-3-gallate, against sevoflurane-induced neuronal apoptosis involve regulation of CREB/BDNF/TrkB and PI3K/Akt/mTOR signalling pathways in neonatal mice

Epigallocatechin-3-gallate (EGCG), a polyphenol in green tea, is an effective antioxidant and possesses neuroprotective effects. Brain-derived neurotrophic factor (BDNF) and cyclic AMP response element-binding protein (CREB) are crucial for neurogenesis and synaptic plasticity. In this study, we aimed to assess the protective effects of EGCG against sevoflurane-induced neurotoxicity in neonatal mice. Distinct groups of C57BL/6 mice were given EGCG (25, 50, or 75 mg/kg body weight) from postnatal day 3 (P3) to P21 and were subjected to sevoflurane (3%; 6 h) exposure on P7. EGCG significantly inhibited sevoflurane-induced neuroapoptosis as determined by Fluoro-Jade B staining and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL). Increased levels of cleaved caspase-3, downregulated Bad and Bax, and significantly enhanced Bcl-2, Bcl-xL, xIAP, c-IAP-1, and survivin expression were observed. EGCG induced activation of the PI3K/Akt pathway as evidenced by increased Akt, phospho-Akt, GSK-3β, phospho-GSK-3β, and mTORc1 levels. Sevoflurane-mediated downregulation of cAMP/CREB and BDNF/TrkB signalling was inhibited by EGCG. Reverse transcription PCR analysis revealed enhanced BDNF and TrkB mRNA levels upon EGCG administration. Improved performance of mice in Morris water maze tests suggested enhanced learning and memory. The study indicates that EGCG was able to effectively inhibit sevoflurane-induced neurodegeneration and improve learning and memory retention of mice via activation of CREB/BDNF/TrkB-PI3K/Akt signalling.

Thromboxane A2 receptor antagonist SQ29548 suppresses the LPS‑induced release of inflammatory cytokines in BV2 microglia cells via suppressing MAPK and NF‑κB signaling pathways

Inflammation in the brain, characterized by the activation of microglia, is hypothesized to participate in the pathogenesis of neuronal disorders. It is proposed that thromboxane A2 receptor (TXA2R) activation is involved in thrombosis/hemostasis and inflammation responses. In the present study, the anti‑inflammatory effects of SQ29548 on lipopolysaccharide (LPS)‑stimulated BV2 microglial cells and its molecular mechanisms were investigated. In the BV2 cell line, LPS‑stimulated nitric oxide (NO) and inflammatory cytokine release, and the phosphorylation of mitogen‑activated protein kinases (MAPKs) and the nuclear factor (NF)‑κB were assessed using an NO assay kit, reverse transcription-quantitative polymerase chain reaction and western blotting, respectively. In vitro studies demonstrated that SQ29548 inhibited LPS‑stimulated BV2 activation and reduced the mRNA expression levels of interleukin (IL)‑1β, IL‑6, tumor necrosis factor‑α and inducible NO synthase via inhibition of MAPKs and the NF‑κB signaling pathway. SQ29548 inhibited the LPS‑induced inflammatory response by blocking MAPKs and NF‑κB activation in BV2 microglial cells.

Recent Advances in the Study of Bipolar/Rod-Shaped Microglia and their Roles in Neurodegeneration

Microglia are the resident immune cells of the central nervous system (CNS) and they contribute to primary inflammatory responses following CNS injuries. The morphology of microglia is closely associated with their functional activities. Most previous research efforts have attempted to delineate the role of ramified and amoeboid microglia in the pathogenesis of neurodegenerative diseases. In addition to ramified and amoeboid microglia, bipolar/rod-shaped microglia were first described by Franz Nissl in 1899 and their presence in the brain was closely associated with the pathology of infectious diseases and sleeping disorders. However, studies relating to bipolar/rod-shaped microglia are very limited, largely due to the lack of appropriate in vitro and in vivo experimental models. Recent studies have reported the formation of bipolar/rod-shaped microglia trains in in vivo models of CNS injury, including diffuse brain injury, focal transient ischemia, optic nerve transection and laser-induced ocular hypertension (OHT). These bipolar/rod-shaped microglia formed end-to-end alignments in close proximity to the adjacent injured axons, but they showed no interactions with blood vessels or other types of glial cell. Recent studies have also reported on a highly reproducible in vitro culture model system to enrich bipolar/rod-shaped microglia that acts as a powerful tool with which to characterize this form of microglia. The molecular aspects of bipolar/rod-shaped microglia are of great interest in the field of CNS repair. This review article focuses on studies relating to the morphology and transformation of microglia into the bipolar/rod-shaped form, along with the differential gene expression and spatial distribution of bipolar/rod-shaped microglia in normal and pathological CNSs. The spatial arrangement of bipolar/rod-shaped microglia is crucial in the reorganization and remodeling of neuronal and synaptic circuitry following CNS injuries. Finally, we discuss the potential neuroprotective roles of bipolar/rod-shaped microglia, and the possibility of transforming ramified/amoeboid microglia into bipolar/rod-shaped microglia. This will be of considerable clinical benefit in the development of novel therapeutic strategies for treating various neurodegenerative diseases and promoting CNS repair after injury.

Involvement of progranulin in modulating neuroinflammatory responses but not neurogenesis in the hippocampus of aged mice

It is well established that adult neurogenesis in the hippocampus declines with age. Our previous studies have suggested that progranulin (PGRN) has a facilitative effect on hippocampal neurogenesis. We have also shown that PGRN plays a role in suppressing excessive neuroinflammatory responses in the cortex and thalamus after brain injury and aging, respectively. However, the roles of PGRN in modulating neurogenesis and neuroinflammatory responses in the hippocampus of aged animals are not yet understood. In the present study, we investigated neurogenesis and neuroinflammation-related responses in the hippocampus of young (15-week-old) and old (135-week-old) wild-type and PGRN-deficient male mice. Neurogenesis in the dentate gyrus of the hippocampus markedly declined with age, and there was no significant difference between the genotype. The number of CD68-positive activated microglia and the expression of lysosomal genes in the hippocampus were significantly increased with age, and PGRN deficiency further increased them. The expression of pro-inflammatory genes was also increased with age, and PGRN deficiency significantly enhanced some of them. These results suggest that PGRN deficiency exacerbates neuroinflammatory responses related to activated microglia in aged animals, while PGRN may not counteract the decline of hippocampal neurogenesis with age.

Spared Nerve Injury Increases the Expression of Microglia M1 Markers in the Prefrontal Cortex of Rats and Provokes Depression-Like Behaviors

Pain and depression are frequently co-existent in clinical practice, yet the underlying mechanisms remain largely to be determined. Microglia activation and subsequent pro-inflammatory responses play a crucial role in the development of neuropathic pain and depression. The process of microglia polarization to the pro-inflammatory M1 or anti-inflammatory M2 phenotypes often occurs during neuroinflammation. However, it remains unclear whether M1/M2 microglia polarization is involved in the neuropathic pain induced by spared nerve injury (SNI). In the present study, the mechanical withdrawal threshold, forced swim test, sucrose preference test, and open field test were performed. The levels of microglia markers including ionized calcium-binding adaptor molecule 1 (Iba1), cluster of differentiation 11b (CD11b), M1 markers including CD68, inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β), IL-6, tumor necrosis factor-a (TNF-α), 8-hydroxy-2-deoxyguanosine (8-OH-dG), and M2 markers including CD206, arginase 1 (Arg1), IL-4 in the prefrontal cortex were determined on day 14 after SNI. The results showed that SNI produced mechanical allodynia and depressive-like behaviors, and also increased the expressions of microglia markers (Iba1, CD11b) and M1 markers (CD68, iNOS, IL-1β, TNF-α, and 8-OH-dG) in the prefrontal cortex. Notably, minocycline administration reversed these abnormalities. In addition, minocycline also promoted M2 microglia polarization as evidenced by up-regulation of CD206 and Arg1. In conclusion, data from our study suggest that SNI can lead to depression-like behaviors, while M1 polarization and consequent overproduction of pro-inflammatory cytokines plays a key role in the pathogenesis of neuropathic pain. The data furthermore indicate that modulation of inflammation by inhibition of M1 polarization could be a strategy for treatment of neuropathic pain, and might prevent the induction of neuropathic pain-induced depression symptoms.

TIR-Domain-Containing Adapter-Inducing Interferon-β (TRIF) Is Essential for MPTP-Induced Dopaminergic Neuroprotection via Microglial Cell M1/M2 Modulation

Dynamic changes of two phenotypes of microglia, M1 and M2, are critically associated with the neurodegeneration of Parkinson's disease. However, the regulation of the M1/M2 paradigm is still unclear. In the MPTP induced neurodegeneration model, we examined the concentration of dopamine (DA) related metabolites and the survival of tyrosine hydroxylase (TH) positive cells in WT and Trif^−/− mice. In in vitro experiments, MN9D cells were co-cultured with BV2 cells to mimic the animal experiments. Inhibition of TRIF aggravated TH+ cell loss, and DA-related metabolites decreased. TRIF inhibition was able to interrupt the microglial M1/M2 dynamic transformation. More BV2 cells were activated and migrated across the membrane of transwell plates by siTRIF treatment. Also, TRIF interruption inhibits the transformation of BV2 cells from the M1 to M2 phenotype which played a beneficial role in neuronal degenerative processes, and increased MN9D apoptosis. Moreover, MPP+ treatment decreases the (DAT) dopamine transporter and TH synthesis by MN9D. Taken together, the current results suggest that TRIF plays a key switch function in contributing to the microglial M1/M2 phenotype dynamic transformation. The interruption of TRIF may decrease the survival of MN9D cells as well as DAT and TH protein production. The current study sheds some light on the PD mechanism research by innate inflammation regulation.

Original article. Patterns of microglial innate immune responses elicited by amyloid β1–42 and lipopolysaccharide: the similarities of the differences

Background: As part of their innate immune response to changes in the central nervous system environment, normally quiescent microglia become activated and increase expression of pattern recognition receptors, scavenger receptors, and production of inflammatory cytokines, proteinases, reactive oxygen species (ROS), and free radicals. These molecules have been implicated in the pathogenesis and progression of several neurodegenerative disorders including Alzheimer disease (AD).

Objective: We compared patterns of microglial innate immune responses elicited by nonfibrillar amyloid β peptide (nfAβ1-42) to those elicited by lipopolysaccharide (LPS).

Methods: Murine BV-2 microglial cells were exposed to either nfAβ1-42 or LPS for 12 h. Then, total RNA from each condition was isolated and expression levels of Toll-like receptor (TLR)-4, scavenger receptor class A (SRMARCO) and class B (SR-BI), CD36, and matrix metalloproteinase (MMP)-9 were determined by reverse transcription-quantitative real-time polymerase chain reaction. The amount of hydrogen peroxide (H2O2) and nitric oxide (NO) in the cell-free supernatant at 24 h were determined using 10-acetyl-3,7-dihydroxyphenoxazine (Amplex Red) and Griess reagent, respectively.

Results: nfAβ1-42 and LPS significantly increased expression of TLR-4, SR-MARCO, CD36, and MMP-9 and production of H2O2 and NO in BV-2 microglial cells compared with that of unstimulated cells. However, expression of SR-BI was significantly induced only when the cells were exposed to nfAβ1-42.

Conclusion: These findings indicate that pattern of microglial innate immune responses elicited by nfAβ1-42 overlap with that elicited by LPS and suggest a specific role of microglial SR-BI expression in AD pathogenesis.

Neuroprotection of Gueichih-Fuling-Wan on cerebral ischemia/ reperfusion injury in streptozotocin-induced hyperglycemic rats via the inhibition of the cellular apoptosis pathway and neuroinflammation

Background: Risks of stroke link with complications of hyperglycemia. Gueichih-Fuling-Wan (GFW), according to Chinese Medical Code literature, has the promotion of blood circulation and attenuates the swollen plot. Recent pharmacological studies have pointed out its efficacy in patients with cerebral ischemia or diabetes. Therefore, this study determined whether GFW has the protection against cerebral ischemia/ reperfusion (I/R) injury in streptozotocin (STZ)-induced hyperglycemic rats and LPS-induced inflammation in BV-2 microglial cells.

Methods: Extracts of GFW were filtered and frozen to dry for use. Hyperglycemia was induced by intraperitoneal injection of 70 mg/kg STZ. Fourteen days after STZ injection, GFW (1, 2 and 4 g/kg) was orally administered once daily for seven days. Rats were subjected to cerebral ischemia/reperfusion and sacrificed for infarction analysis and neuronal apoptosis detection twenty-one days after STZ injection. MTT assay was used for cell viability; nitrite quantification and western blot analysis of iNOS and COX-2 were used to explore the effects of GFW on LPS-induced inflammation in BV-2 microglial cells.

Results: GFW significantly ameliorated cerebral infarction while dosage was more than 1 g/kg (by 38.03% at 2 g/kg and 52.44% at 4 g/kg), and attenuated neurological deficits by 23.48% (at 2 g/kg) and 47.25% (at 4 g/kg). Furthermore, GFW (2, 4 g/kg) notably decreased TUNEL- and cleaved caspase-3-positive cells in the immunohistochemical stain (P < 0.01 and P < 0.001, respectively). GFW remarkably increased in Bcl-2 and decreased in caspase-3 and Bax/Bcl-2 ratio protein expressions by Western blot. GFW (0.25, 0.5, 1 mg/ ml) significantly reduced LPS-induced NO production in BV-2 microglial cells. And GFW attenuated iNOS and COX-2 expression in LPS-treated BV-2 cells. Conclusions: In summary, GFW has good bioactivities to protect cerebral I/R injury in hyperglycemic rats, which might be due to inhibition of cellular apoptosis and neuroinflammation.

Neurodegenerative Diseases: Might Citrus Flavonoids Play a Protective Role?

Neurodegenerative diseases (ND) result from the gradual and progressive degeneration of the structure and function of the central nervous system or the peripheral nervous system or both. They are characterized by deterioration of neurons and/or myelin sheath, disruption of sensory information transmission and loss of movement control. There is no effective treatment for ND, and the drugs currently marketed are symptom-oriented, albeit with several side effects. Within the past decades, several natural remedies have gained attention as potential neuroprotective drugs. Moreover, an increasing number of studies have suggested that dietary intake of vegetables and fruits can prevent or delay the onset of ND. These properties are mainly due to the presence of polyphenols, an important group of phytochemicals that are abundantly present in fruits, vegetables, cereals and beverages. The main class of polyphenols is flavonoids, abundant in Citrus fruits. Our review is an overview on the scientific literature concerning the neuroprotective effects of the Citrus flavonoids in the prevention or treatment of ND. This review may be used as scientific basis for the development of nutraceuticals, food supplements or complementary and alternative drugs to maintain and improve the neurophysiological status.

Biochanin A Protects Against Lipopolysaccharide-Induced Damage of Dopaminergic Neurons Both In Vivo and In Vitro via Inhibition of Microglial Activation

Neuroinflammation has been reported to be involved in the pathogenesis of Parkinson's disease (PD). Inhibition of microglia-mediated neuroinflammation might be a potential strategy for PD treatment. Biochanin A, is an O-methylated isoflavone, classified as a kind of phytoestrogens due to its chemical structure that is similar to mammalian estrogens. It has been found to possess antifibrotic, antiapoptotic, and antioxidant effects. In the present study, we investigated the neuroprotective effects of biochanin A on lipopolysaccharide (LPS)-induced dopaminergic neurons damage both in vivo and in vitro and the related molecular mechanisms. The results showed that biochanin A treatment for 21 days significantly attenuated the behavioral dysfunction of PD rats, prevented dopaminergic neurons damage, and inhibited activation of microglia in the LPS-induced PD rats. Furthermore, biochanin A decreased the levels of interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in the serum, and inhibited the phosphorylation of ERK, JNK, p38 in the substantia nigra of PD rats. In vitro test, biochanin A also inhibited primary microglial activation and protected dopaminergic neurons, decreased the content of nitric oxide, IL-1β, and TNF-α in supernatants, and inhibited the reactive oxygen species production. Taken together, these results suggest that biochanin A exerts protective effects on LPS-induced PD rats, and the mechanisms may be associated with the inhibition of inflammatory response and the MAPK signaling pathway.