Role of Microglia TLRs in Neurodegeneration

The Neuromelanin Paradox and Its Dual Role in Oxidative Stress and Neurodegeneration

Aging is associated with an increasing dysfunction of key brain homeostasis mechanisms and represents the main risk factor across most neurodegenerative disorders. However, the degree of dysregulation and the affectation of specific pathways set apart normal aging from neurodegenerative disorders. In particular, the neuronal metabolism of catecholaminergic neurotransmitters appears to be a specifically sensitive pathway that is affected in different neurodegenerations. In humans, catecholaminergic neurons are characterized by an age-related accumulation of neuromelanin (NM), rendering the soma of the neurons black. This intracellular NM appears to serve as a very efficient quencher for toxic molecules. However, when a neuron degenerates, NM is released together with its load (many undegraded cellular components, transition metals, lipids, xenobiotics) contributing to initiate and worsen an eventual immune response, exacerbating the oxidative stress, ultimately leading to the neurodegenerative process. This review focuses on the analysis of the role of NM in normal aging and neurodegeneration related to its capabilities as an antioxidant and scavenging of harmful molecules, versus its involvement in oxidative stress and aberrant immune response, depending on NM saturation state and its extracellular release.

Functions and Therapeutic Potential of Extracellular Hsp60, Hsp70, and Hsp90 in Neuroinflammatory Disorders

Neuroinflammation is implicated in central nervous system (CNS) diseases, but the molecular mechanisms involved are poorly understood. Progress may be accelerated by developing a comprehensive view of the pathogenesis of CNS disorders, including the immune and the chaperone systems (IS and CS). The latter consists of the molecular chaperones; cochaperones; and chaperone cofactors, interactors, and receptors of an organism and its main collaborators in maintaining protein homeostasis (canonical function) are the ubiquitin–proteasome system and chaperone-mediated autophagy. The CS has also noncanonical functions, for instance, modulation of the IS with induction of proinflammatory cytokines. This deserves investigation because it may be at the core of neuroinflammation, and elucidation of its mechanism will open roads toward developing efficacious treatments centered on molecular chaperones (i.e., chaperonotherapy). Here, we discuss information available on the role of three members of the CS—heat shock protein (Hsp)60, Hsp70, and Hsp90—in IS modulation and neuroinflammation. These three chaperones occur intra- and extracellularly, with the latter being the most likely involved in neuroinflammation because they can interact with the IS. We discuss some of the interactions, their consequences, and the molecules involved but many aspects are still incompletely elucidated, and we hope that this review will encourage research based on the data presented to pave the way for the development of chaperonotherapy. This may consist of blocking a chaperone that promotes destructive neuroinflammation or replacing or boosting a defective chaperone with cytoprotective activity against neurodegeneration.

Antiallergic drug desloratadine as a selective antagonist of 5HT2A receptor ameliorates pathology of Alzheimer's disease model mice by improving microglial dysfunction

Alzheimer's disease (AD) is a progressively neurodegenerative disease characterized by cognitive deficits and alteration of personality and behavior. As yet, there is no efficient treatment for AD. 5HT_2A receptor (5HT_2A R) is a subtype of 5HT₂ receptor belonging to the serotonin receptor family, and its antagonists have been clinically used as antipsychotics to relieve psychopathy. Here, we discovered that clinically first-line antiallergic drug desloratadine (DLT) functioned as a selective antagonist of 5HT_2A R and efficiently ameliorated pathology of APP/PS1 mice. The underlying mechanism has been intensively investigated by assay against APP/PS1 mice with selective 5HT_2A R knockdown in the brain treated by adeno-associated virus (AAV)-ePHP-si-5HT_2A R. DLT reduced amyloid plaque deposition by promoting microglial Aβ phagocytosis and degradation, and ameliorated innate immune response by polarizing microglia to an anti-inflammatory phenotype. It stimulated autophagy process and repressed neuroinflammation through 5HT_2A R/cAMP/PKA/CREB/Sirt1 pathway, and activated glucocorticoid receptor (GR) nuclear translocation to upregulate the transcriptions of phagocytic receptors TLR2 and TLR4 in response to microglial phagocytosis stimulation. Together, our work has highly supported that 5HT_2A R antagonism might be a promising therapeutic strategy for AD and highlighted the potential of DLT in the treatment of this disease.

Circadian changes in Alzheimer's disease: Neurobiology, clinical problems, and therapeutic opportunities

The understanding of Alzheimer's disease (AD) pathophysiology is an active area of research, and the traditional focus on hippocampus, amyloid and tau protein, and memory impairment has been expanded with components like neuroinflammation, insulin resistance, and circadian rhythm alterations. The bidirectional vicious cycle of neuroinflammation and neurodegeneration on a molecular level may cause functional deficits already long before the appearance of overt clinical symptoms. Located at the crossroads of metabolic, circadian, and hormonal signaling, the hypothalamus has been identified as another brain region affected by AD pathophysiology. Current findings on hypothalamic dysfunction open a broader horizon for studying AD pathogenesis and offer new opportunities for diagnosis and therapy. While treatments with cholinomimetics and memantine form a first line of pharmacological treatment, additional innovative research is pursued toward the development of antiinflammatory, growth factor, or antidiabetic types of medication. Following recent epidemiological data showing associations of AD incidence with modern societal and "life-style"-related risk factors, also nonpharmacological interventions, including sleep optimization, are being developed and some have been shown to be beneficial. Circadian aspects in AD are relevant from a pathophysiological standpoint, but they can also have an important role in pharmacologic and nonpharmacologic interventions, and appropriate timing of sleep, meals, and medication may boost therapeutic efficacy.

The Gut-Brain Axis in Autism Spectrum Disorder: A Focus on the Metalloproteases ADAM10 and ADAM17

Autism Spectrum Disorder (ASD) is a spectrum of disorders that are characterized by problems in social interaction and repetitive behavior. The disease is thought to develop from changes in brain development at an early age, although the exact mechanisms are not known yet. In addition, a significant number of people with ASD develop problems in the intestinal tract. A Disintegrin And Metalloproteases (ADAMs) include a group of enzymes that are able to cleave membrane-bound proteins. ADAM10 and ADAM17 are two members of this family that are able to cleave protein substrates involved in ASD pathogenesis, such as specific proteins important for synapse formation, axon signaling and neuroinflammation. All these pathological mechanisms are involved in ASD. Besides the brain, ADAM10 and ADAM17 are also highly expressed in the intestines. ADAM10 and ADAM17 have implications in pathways that regulate gut permeability, homeostasis and inflammation. These metalloproteases might be involved in microbiota-gut-brain axis interactions in ASD through the regulation of immune and inflammatory responses in the intestinal tract. In this review, the potential roles of ADAM10 and ADAM17 in the pathology of ASD and as targets for new therapies will be discussed, with a focus on the gut-brain axis.

Transcriptomic characterization of microglia activation in a rat model of ischemic stroke

Microglia are key regulators of inflammatory response after stroke and brain injury. To better understand activation of microglia as well as their phenotypic diversity after ischemic stroke, we profiled the transcriptome of microglia after 75 min transient focal cerebral ischemia in 3-month- and 12-month-old male spontaneously hypertensive rats. Microglia were isolated from the brains by FACS sorting on days 3 and 14 after cerebral ischemia. GeneChip Rat 1.0ST microarray was used to profile the whole transcriptome of sorted microglia. We identified an evolving and complex pattern of activation from 3 to 14 days after stroke onset. M2-like patterns were extensively and persistently upregulated over time. M1-like patterns were only mildly upregulated, mostly at day 14. Younger 3-month-old brains showed a larger microglial response in both pro- and anti-inflammatory pathways, compared to older 12-month-old brains. Importantly, our data revealed that after stroke, most microglia are activated towards a wide spectrum of novel polarization states beyond the standard M1/M2 dichotomy, especially in pathways related to TLR2 and dietary fatty acid signaling. Finally, classes of transcription factors that might potentially regulate microglial activation were identified. These findings should provide a comprehensive database for dissecting microglial mechanisms and pursuing neuroinflammation targets for acute ischemic stroke.

SP1 activated-lncRNA SNHG1 mediates the development of epilepsy via miR-154-5p/TLR5 axis

BACKGROUND

Epilepsy is a one of the most frequent serious neurological disorders characterized by enduring and unprovoked seizures. The treatments to epilepsy are very limited and many patients are even resistant to current medications due to the elusive pathogenesis. Here, we sought to investigate the functions of lncRNA SNHG1 and miR-154-5p in epilepsy.

METHODS

We employed both in vivo mouse model and in vitro cell model to study epilepsy. H&E staining and Nissl staining were used to examine the morphology of hippocampus and measure neuronal injury, respectively. TUNEL staining and flow cytometry were performed to determine cell apoptosis. Caspase-3 activity assay kit was used to assess caspase-3 activity. RT-qPCR and western blot were conducted to measure the levels of SNHG1, miR-154-5p, TLR5, and SP1, respectively. Dual luciferase reporter assay was employed to validate the binding relationship of SNHG1/miR-154-5p and miR-154-5p/TLR5. ChIP assay was performed to confirm the transcriptional regulation of SP1 on SNHG1.

RESULTS

Elevated SNHG1 and decreased miR-154-5p were observed in both in vivo mouse model and in vitro cell model of epilepsy. Knockdown of SNHG1 or transfection with miR-154-5p mimics significantly ameliorated Mg2+ free-induced neuronal injury in SH-SY5Y cells. SNHG1 acted as a sponge of miR-154-5p. Moreover, SNHG1 promoted neuronal injury via acting as a miR-154-5p sponge to disinhibit TLR5. Additionally, SP1 activated the transcriptional activity of SNHG1.

CONCLUSION

In summary, SP1 transcriptionally activated-SNHG1 contributes to the development of epilepsy via directly regulating miR-154-5p/TLR5 axis, which provides novel targets in treatment of epilepsy.

Astrocyte-Oligodendrocyte-Microglia Crosstalk in Astrocytopathies

Defective astrocyte function due to a genetic mutation can have major consequences for microglia and oligodendrocyte physiology, which in turn affects the white matter integrity of the brain. This review addresses the current knowledge on shared and unique pathophysiological mechanisms of astrocytopathies, including vanishing white matter, Alexander disease, megalencephalic leukoencephalopathy with subcortical cysts, Aicardi-Goutières syndrome, and oculodentodigital dysplasia. The mechanisms of disease include protein accumulation, unbalanced secretion of extracellular matrix proteins, pro- and anti-inflammatory molecules, cytokines and chemokines by astrocytes, as well as an altered gap junctional network and a changed ionic and nutrient homeostasis. Interestingly, the extent to which astrogliosis and microgliosis are present in these astrocytopathies is highly variable. An improved understanding of astrocyte-microglia-oligodendrocyte crosstalk might ultimately lead to the identification of druggable targets for these, currently untreatable, severe conditions.

Pro-Inflammatory Role of AQP4 in Mice Subjected to Intrastriatal Injections of the Parkinsonogenic Toxin MPP

Aquaporin-4 (AQP4) is critically involved in brain water and volume homeostasis and has been implicated in a wide range of pathological conditions. Notably, evidence has been accrued to suggest that AQP4 plays a proinflammatory role by promoting release of astrocytic cytokines that activate microglia and other astrocytes. Neuroinflammation is a hallmark of Parkinson’s disease (PD), and we have previously shown that astrocytes in substantia nigra (SN) are enriched in AQP4 relative to cortical astrocytes, and that their complement of AQP4 is further increased following treatment with the parkinsonogenic toxin MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine). Here, we investigated the effect of Aqp4 deletion on microglial activation in mice subjected to unilateral intrastriatal injection of 1-methyl-4-phenylpyridinium (MPP+, the toxic metabolite of MPTP). Our results show that MPP+ injections lead to a pronounced increase in the expression level of microglial activating genes in the ventral mesencephalon of wild type (WT) mice, but not Aqp4^−/− mice. We also show, in WT mice, that MPP+ injections cause an upregulation of nigral AQP4 and swelling of astrocytic endfeet. These findings are consistent with the idea that AQP4 plays a pro-inflammatory role in Parkinson’s disease, secondary to the dysregulation of astrocytic volume homeostasis.

Do the Bugs in Your Gut Eat Your Memories? Relationship between Gut Microbiota and Alzheimer's Disease

The human microbiota is composed of trillions of microbial cells inhabiting the oral cavity, skin, gastrointestinal (GI) tract, airways, and reproductive organs. The gut microbiota is composed of dynamic communities of microorganisms that communicate bidirectionally with the brain via cytokines, neurotransmitters, hormones, and secondary metabolites, known as the gut microbiota-brain axis. The gut microbiota-brain axis is suspected to be involved in the development of neurological diseases, including Alzheimer's disease (AD), Parkinson's disease, and Autism Spectrum Disorder. AD is an irreversible, neurodegenerative disease of the central nervous system (CNS), characterized by amyloid-β plaques, neurofibrillary tangles, and neuroinflammation. Microglia and astrocytes, the resident immune cells of the CNS, play an integral role in AD development, as neuroinflammation is a driving factor of disease severity. The gut microbiota-brain axis is a novel target for Alzheimer's disease therapeutics to modulate critical neuroimmune and metabolic pathways. Potential therapeutics include probiotics, prebiotics, fecal microbiota transplantation, and dietary intervention. This review summarizes our current understanding of the role of the gut microbiota-brain axis and neuroinflammation in the onset and development of Alzheimer's disease, limitations of current research, and potential for gut microbiota-brain axis targeted therapies.

Blood Transcriptome Response to Environmental Metal Exposure Reveals Potential Biological Processes Related to Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease which is manifested by a progressive and irreversible decline of cognition, memory loss, a shortened attention span, and changes in personality. Aging and genetic pre-dispositions, particularly the presence of a specific form of apolipoprotein E (APOE), are main risk factors of sporadic AD; however, a large body of evidence has shown that multiple environmental factors, including exposure to toxic metals, increase the risk for late onset AD. Lead (Pb) and cadmium (Cd) are ubiquitous toxic metals with a wide range of applications resulting in global distribution in the environment and exposure of all living organisms on earth. In addition to being classified as carcinogenic (Cd) and possibly carcinogenic (Pb) to humans by the International Agency for Research on Cancer, both compounds disrupt metal homeostasis and can cause toxic responses at the cellular and organismal levels. Pb toxicity targets the central nervous system and evidence for that has emerged also for Cd. Recent epidemiological studies show that both metals possibly are etiological factors of multiple neurodegenerative diseases, including Alzheimer's disease (AD). To further explore the association between metal exposure and AD risk we applied whole transcriptome gene expression analysis in peripheral blood leukocytes (PBLs) from 632 subjects of the general population, taken from the EnviroGenomarkers project. We used linear mixed effect models to associate metal exposure to gene expression after adjustment for gender, age, BMI, smoking, and alcohol consumption. For Pb exposure only few associations were identified, including a downregulation of the human eukaryotic translation initiation factor 5 (eIF5). In contrast, Cd exposure, particularly in males, revealed a much stronger transcriptomic response, featuring multiple pathways related to pathomolecular mechanisms of AD, such as endocytosis, neutrophil degranulation, and Interleukin-7 signaling. A gender stratified analysis revealed that the Cd responses were male-specific and included a downregulation of the APOE gene in men. This exploratory study revealed novel hypothetical findings which might contribute to the understanding of the neurotoxic effects of chronic Pb and Cd exposure and possibly improve our knowledge on the molecular mechanisms linking metal exposure to AD risk.

Loss of the neuronal genome organizer and transcription factor CTCF induces neuronal death and reactive gliosis in the anterior cingulate cortex

CCCTC-binding factor (CTCF) is a genome organizer that regulates gene expression through transcription and chromatin structure regulation. CTCF also plays an important role during the developmental and adult stages. Cell-specific CTCF deletion studies have shown that a reduction in CTCF expression leads to the development of distinct clinical features and cognitive disorders. Therefore, we knocked out Ctcf (CTCF cKO) in the excitatory neurons of the forebrain in a Camk2a-Cre mouse strain to examine the role of CTCF in cell death and gliosis in the cortex. CTCF cKO mice were viable, but they demonstrated an age-dependent increase in reactive gliosis of astrocytes and microglia in the anterior cingulate cortex (ACC) from 16 weeks of age prior to neuronal loss observed at over 20 weeks of age. Consistent with these data, qRT-PCR analysis of the CTCF cKO ACC revealed changes in the expression of inflammation-related genes (Hspa1a, Prokr2 and Itga8) linked to gliosis and neuronal death. Our results suggest that prolonged Ctcf gene deficiency in excitatory neurons results in neuronal cell death and gliosis, possibly through functional changes in inflammation-related genes.

Sex-Specific Cognitive Deficits Following Space Radiation Exposure

The radiation fields in space define tangible risks to the health of astronauts, and significant work in rodent models has clearly shown a variety of exposure paradigms to compromise central nervous system (CNS) functionality. Despite our current knowledge, sex differences regarding the risks of space radiation exposure on cognitive function remain poorly understood, which is potentially problematic given that 30% of astronauts are women. While work from us and others have demonstrated pronounced cognitive decrements in male mice exposed to charged particle irradiation, here we show that female mice exhibit significant resistance to adverse neurocognitive effects of space radiation. The present findings indicate that male mice exposed to low doses (≤30 cGy) of energetic (400 MeV/n) helium ions (⁴He) show significantly higher levels of neuroinflammation and more extensive cognitive deficits than females. Twelve weeks following ⁴He ion exposure, irradiated male mice demonstrated significant deficits in object and place recognition memory accompanied by activation of microglia, marked upregulation of hippocampal Toll-like receptor 4 (TLR4), and increased expression of the pro-inflammatory marker high mobility group box 1 protein (HMGB1). Additionally, we determined that exposure to ⁴He ions caused a significant decline in the number of dendritic branch points and total dendritic length along with the hippocampus neurons in female mice. Interestingly, only male mice showed a significant decline of dendritic spine density following irradiation. These data indicate that fundamental differences in inflammatory cascades between male and female mice may drive divergent CNS radiation responses that differentially impact the structural plasticity of neurons and neurocognitive outcomes following cosmic radiation exposure.

Modulation of the Innate Immune Response by Targeting Toll-like Receptors: A Perspective on Their Agonists and Antagonists

Toll-like receptors (TLRs) are a class of proteins that recognize pathogen-associated molecular patterns (PAMPs) and damaged-associated molecular patterns (DAMPs), and they are involved in the regulation of innate immune system. These transmembrane receptors, localized at the cellular or endosomal membrane, trigger inflammatory processes through either myeloid differentiation primary response 88 (MyD88) or TIR-domain-containing adapter-inducing interferon-β (TRIF) signaling pathways. In the last decades, extensive research has been performed on TLR modulators and their therapeutic implication under several pathological conditions, spanning from infections to cancer, from metabolic disorders to neurodegeneration and autoimmune diseases. This Perspective will highlight the recent discoveries in this field, emphasizing the role of TLRs in different diseases and the therapeutic effect of their natural and synthetic modulators, and it will discuss insights for the future exploitation of TLR modulators in human health.

Microglia-targeting nanotherapeutics for neurodegenerative diseases

Advances in nanotechnology have enabled the design of nanotherapeutic platforms that could address the challenges of targeted delivery of active therapeutic agents to the central nervous system (CNS). While the majority of previous research studies on CNS nanotherapeutics have focused on neurons and endothelial cells, the predominant resident immune cells of the CNS, microglia, are also emerging as a promising cellular target for neurodegeneration considering their prominent role in neuroinflammation. Under normal physiological conditions, microglia protect neurons by removing pathological agents. However, long-term exposure of microglia to stimulants will cause sustained activation and lead to neuronal damage due to the release of pro-inflammatory agents, resulting in neuroinflammation and neurodegeneration. This Perspective highlights criteria to be considered when designing microglia-targeting nanotherapeutics for the treatment of neurodegenerative disorders. These criteria include conjugating specific microglial receptor-targeting ligands or peptides to the nanoparticle surface to achieve targeted delivery, leveraging microglial phagocytic properties, and utilizing biocompatible and biodegradable nanomaterials with low immune reactivity and neurotoxicity. In addition, certain therapeutic agents for the controlled inhibition of toxic protein aggregation and for modulation of microglial activation pathways can also be incorporated within the nanoparticle structure without compromising stability. Overall, considering the multifaceted disease mechanisms of neurodegeneration, microglia-targeted nanodrugs and nanotherapeutic particles may have the potential to resolve multiple pathological determinants of the disease and to guide a shift in the microglial phenotype spectrum toward a more neuroprotective state.

Role of Toll Like Receptor 4 in Alzheimer's Disease

Long-term evidence has confirmed the involvement of an inflammatory component in neurodegenerative disorders including Alzheimer’s disease (AD). This view is supported, in part, by data suggesting that selected non-steroidal anti-inflammatory drugs (NSAIDs) provide protection. Additionally, molecular players of the innate immune system have recently been proposed to contribute to these diseases. Toll-like receptors (TLRs) are transmembrane pattern-recognition receptors of the innate immune system that recognize different pathogen-derived and tissue damage-related ligands. TLR4 mediated signaling has been reported to contribute to the pathogenesis of age-related neurodegenerative diseases, including AD. Although the pathophysiology of AD is not clear, soluble aggregates (oligomers) of the amyloid β peptide (Aβo) have been proven to be key players in the pathology of AD. Among others, Aβo promote Ca²⁺ entry and mitochondrial Ca²⁺ overload leading to cell death in neurons. TLR4 has recently been found to be involved in AD but the mechanisms are unclear. Our group recently reported that lipopolysaccharide (LPS), a TLR4 receptor agonist, increases cytosolic Ca²⁺ concentration leading to apoptosis. Strikingly, this effect was only observed in long-term cultured primary neurons considered a model of aging neurons, but not in short-term cultured neurons resembling young neurons. These effects were significantly prevented by pharmacological blockade of TLR4 receptor signaling. Moreover, TLR4 expression in rat hippocampal neurons increased significantly in aged neurons in vitro. Therefore, molecular patterns associated with infection and/or brain cell damage may activate TLR4 and Ca²⁺ signaling, an effect exacerbated during neuronal aging. Here, we briefly review the data regarding the involvement of TLR4 in AD.

The potential role of nanoyttria in alleviating oxidative stress biomarkers: Implications for Alzheimer's disease therapy

Alzheimer's disease (AD) is a fatal neurodegenerative disease that requires immediate attention. Oxidative stress that leads to the generation of reactive oxygen species is a contributing factor to the disease progression by promoting synthesis and deposition of amyloid-β, the main hallmark protein in AD. It has been previously demonstrated that nanoyttria possesses antioxidant properties and can alleviate cellular oxidative injury in various toxicity and disease models. This review proposed that nanoyttria could be used for the treatment of AD. In this paper, the evidence on the antioxidant potential of nanoyttria is presented and its prospects on AD therapy are discussed.

Aging and sex: Impact on microglia phagocytosis

Microglia dysfunction and activation are important hallmarks of the aging brain and are concomitant with age-related neurodegeneration and cognitive decline. Age-associated changes in microglia migration and phagocytic capacity result in maladaptive responses, chronic neuroinflammation, and worsened outcomes in neurodegenerative disorders. Given the sex bias in the incidence, prevalence, and therapy response of most neurological disorders, we have here examined whether the phagocytic activity of aged microglia is different in males and females. With this aim, the phagocytosis activity of male and female cells was compared in an in vitro aged microglia model and in microglia isolated from adult (5-month-old) or aged (18-month-old) mice. In both models, the phagocytosis of neural debris increased with aging in male and female cells and was higher in aged female microglia than in aged male cells. However, female aged microglia lost its ability to adapt its phagocytic activity to inflammatory conditions. These findings suggest that microglia phagocytosis of neural debris may represent a previously unexplored neuroprotective characteristic of aged microglia that may contribute to the generation of sex differences in the manifestation of neurodegenerative diseases.

Glia Crosstalk in Neuroinflammatory Diseases

Neuroinflammation constitutes a fundamental cellular process to signal the loss of brain homeostasis. Glial cells play a central role in orchestrating these neuroinflammation processes in both deleterious and beneficial ways. These cellular responses depend on their intercellular interactions with neurons, astrocytes, the blood–brain barrier (BBB), and infiltrated T cells in the central nervous system (CNS). However, this intercellular crosstalk seems to be activated by specific stimuli for each different neurological scenario. This review summarizes key studies linking neuroinflammation with certain neurodegenerative diseases such as Alzheimer disease (AD), Parkinson disease (PD), and amyotrophic lateral sclerosis (ALS) and for the development of better therapeutic strategies based on immunomodulation.

Neuroinflammation is associated with infiltration of T cells in Lewy body disease and α-synuclein transgenic models

BACKGROUND

α-Synuclein (α-syn) is a pre-synaptic protein which progressively accumulates in neuronal and non-neuronal cells in neurodegenerative diseases such as Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy. Recent evidence suggests that aberrant immune activation may be involved in neurodegeneration in PD/DLB. While previous studies have often focused on the microglial responses, less is known about the role of the peripheral immune system in these disorders.

METHODS

To understand the involvement of the peripheral immune system in PD/DLB, we evaluated T cell populations in the brains of α-syn transgenic (tg) mice (e.g., Thy1 promoter line 61) and DLB patients.

RESULTS

Immunohistochemical analysis showed perivascular and parenchymal infiltration by CD3+/CD4+ helper T cells, but not cytotoxic T cells (CD3+/CD8+) or B cells (CD20+), in the neocortex, hippocampus, and striatum of α-syn tg mice. CD3+ cells were found in close proximity to the processes of activated astroglia, particularly in areas of the brain with significant astrogliosis, microgliosis, and expression of pro-inflammatory cytokines. In addition, a subset of CD3+ cells co-expressed interferon γ. Flow cytometric analysis of immune cells in the brains of α-syn tg mice revealed that CD1d-tet+ T cells were also increased in the brains of α-syn tg mice suggestive of natural killer T cells. In post-mortem DLB brains, we similarly detected increased numbers of infiltrating CD3+/CD4+ T cells in close proximity with blood vessels.

CONCLUSION

These results suggest that infiltrating adaptive immune cells play an important role in neuroinflammation and neurodegeneration in synucleinopathies and that modulating peripheral T cells may be a viable therapeutic strategy for PD/DLB.

Microglia: Agents of the CNS Pro-Inflammatory Response

The pro-inflammatory immune response driven by microglia is a key contributor to the pathogenesis of several neurodegenerative diseases. Though the research of microglia spans over a century, the last two decades have increased our understanding exponentially. Here, we discuss the phenotypic transformation from homeostatic microglia towards reactive microglia, initiated by specific ligand binding to pattern recognition receptors including toll-like receptor-4 (TLR4) or triggering receptors expressed on myeloid cells-2 (TREM2), as well as pro-inflammatory signaling pathways triggered such as the caspase-mediated immune response. Additionally, new research disciplines such as epigenetics and immunometabolism have provided us with a more holistic view of how changes in DNA methylation, microRNAs, and the metabolome may influence the pro-inflammatory response. This review aimed to discuss our current knowledge of pro-inflammatory microglia from different angles, including recent research highlights such as the role of exosomes in spreading neuroinflammation and emerging techniques in microglia research including positron emission tomography (PET) scanning and the use of human microglia generated from induced pluripotent stem cells (iPSCs). Finally, we also discuss current thoughts on the impact of pro-inflammatory microglia in neurodegenerative diseases.

Erythronium japonicum Alleviates Inflammatory Pain by Inhibiting MAPK Activation and by Suppressing NF-κB Activation via ERK/Nrf2/HO-1 Signaling Pathway

Microglial activation-mediated neuroinflammation influences the development of inflammatory pain. The aim of this study was to investigate the anti-inflammatory effects and mechanisms of aqueous Erythronium japonicum extract (EJE) in microglia activation-mediated inflammatory pain. EJE was found to suppress lipopolysaccharide (LPS)-induced inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), ionized calcium-binding adapter molecule 1 (IBA-1), and pro-inflammatory cytokines in BV2 microglial cells. In addition, LPS-induced c-Jun NH₂ terminal protein kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) phosphorylation were inhibited by EJE. Intriguingly, EJE also inhibited p65 phosphorylation by activating extracellular signal-regulated kinase-1/2 (ERK)/nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling. Furthermore, the effects of EJE treatment, such as HO-1 induction and the reduction of NF-ĸB activation, were reversed by ERK1/2 inhibition. In an inflammatory pain mouse model, Complete Freund’s Adjuvant (CFA)-induced mechanical allodynia and foot swelling were alleviated by the oral administration of EJE. Consistent with in vitro results, EJE increased HO-1, while decreasing CFA-induced COX-2, IBA-1, and pro-inflammatory cytokines in the spinal cord. Among the components of EJE, butanol most heavily suppressed LPS-induced microglial activation and increased HO-1 expression. These findings indicate that EJE can alleviate inflammatory pain by inhibiting p38 and JNK and by suppressing NF-ĸB via ERK/Nrf2/HO-1 signaling.

Banhasasim-Tang Attenuates Lipopolysaccharide-Induced Cognitive Impairment by Suppressing Neuroinflammation in Mice

Banhasasim-tang (BHS) is an herbal medicine that has been widely used in East Asia to treat various symptoms associated with upper abdomen swelling. BHS has not been studied previously for neuroinflammation or cognitive disorder. Here, we use a lipopolysaccharide (LPS) model to investigate the effects and mechanisms of BHS in neuroinflammation and cognitive impairment of mice. We used a mouse model of LPS-induced cognitive impairment and neuroinflammation and examined whether administration of BHS prevents these deficits via Morris water maze test, passive avoidance test, histopathological analysis, Western blotting, and real-time reverse transcription polymerase chain reaction (RT-qPCR). We found via behavioral tests that BHS treatment effectively prevented LPS-induced memory loss and neuronal damage in mice. Histopathological analysis of mouse brains revealed that BHS inhibited LPS-induced expression of microglial and astrocyte activation markers. Furthermore, BHS inhibits the production of markers related to neurodegeneration, amyloidogenesis, and inflammation, and mRNA expression of inflammatory mediators in mouse brain tissue. Additionally, BHS pretreatment effectively inhibited generation of inflammatory factors and pathways in BV2 microglial cells stimulated by LPS. These observations indicate that BHS is effective in preventing cognitive impairment caused by neuroinflammation and has strong potential as a candidate treatment for neuronal inflammatory diseases.

Targeting the innate immune receptor TLR8 using small-molecule agents

Toll-like receptors (TLRs) are pattern-recognition receptors that initiate innate immune responses. Among the TLRs, TLR8 (and TLR7) recognizes single-stranded RNA to mediate downstream signals. In recent years, intensive X-ray crystal structural analyses have provided atomic insights into structures of TLR8 complexed with various agonists or antagonists. Here, structural knowledge of the activation and inactivation mechanisms of the ligands is reviewed. In addition, the potential clinical applications of TLR ligands are examined.

Remodeling microglia to a protective phenotype in Parkinson's disease?

Parkinson's disease (PD) is the most widespread movement disorder with a prevalence of 1 in 1000 individuals above 60 years of age. Until now, understanding the pathological mechanisms of PD to translate them into therapy has remained a high research priority. In this review, we highlight evidence describing the involvement of microglial dysfunction in PD. Thereafter, we provide current knowledge suggesting that the substantia nigra pars compacta and putamen, compared to other brain regions, show a reduced microglial density, as well as altered morphological and functional properties in homeostatic conditions, while presenting dystrophic features associated with aging. Further, we describe that this defective microglial programing emerges as early as the second postnatal week, persists until adulthood and impacts negatively on their transcriptional pattern and provision of local trophic support. We emphasize the role of α-synuclein oligomers as a major dysfunctional signal underlining microglial-mediated phenotypic switch and adaptive response contributing to neurodegeneration. Moreover, we explore available avenues should microglia be considered as target for neuroprotective or restorative strategies including preventing the aggregation of α-synuclein protofibrils formation. However, we provide a note of caution regarding the success of microglial-targeted PD strategies, using minocycline as an example. In conclusion, we discuss putative neuroprotective agents that were unsuccessful in previous trials but could be reconsidered by focusing on the stage of microglial-dependent pathogenic events during PD in suitable cohorts of patients.

Characterising lipoteichoic acid as an in vitro model of acute neuroinflammation

Toll-like receptor 2 (TLR2) is a primary sensor for pathogens, including those derived from gram-positive bacteria. It can also mediate the effects of endogenous inflammatory signals such as β-amyloid peptide (Aβ), thus promoting the microglial activation and subsequent neuronal dysfunction, characteristic of chronic neuroinflammatory conditions. More recently, a role for TLR2 has been proposed in the pathogenesis of disorders associated with acute inflammation, including anxiety and depression. The current study aims to characterise the acute effects of the TLR2 agonist lipoteichoic acid (LTA) on microglial activation and neuronal integrity, and to evaluate the influence of LTA exposure on sensitivity to the inflammation and neuronal dysfunction associated with Aβ. Using BV2 and N2a cells as an in vitro model, we highlight that acute exposure to LTA robustly promotes inflammatory cytokine and nitric oxide (NO) production in microglia but also in neurons, similar to that reported under longer-term and chronic inflammatory conditions. Moreover, we find that exposure to LTA can enhance sensitivity to subthreshold Aβ, promoting an 'M1'-like phenotype in microglia and provoking dysregulation of neuronal activity in acute hippocampal slices. Anti-inflammatory agents, including mimetics of brain-derived neurotrophic factor (BDNF), have proven effective at alleviating chronic neuroinflammatory complications. We further examined the effects of 7,8,3-trihydroxyflavone (7,8,3-THF), a small-molecule TrkB agonist, on LTA-induced microglial activation. We report that 7,8,3-THF can significantly ameliorate interleukin (IL)-6 and NO production in LTA-stimulated BV2 cells. Taken together, our findings offer support for exploration of TLR2 as a potential target for therapeutic intervention into acute neuroinflammatory conditions. Moreover we propose that exposure to gram-positive bacterial pathogens may promote sensitivity to the inflammatory changes characteristic of the aged brain.

Diagnostic performance of new and classic CSF biomarkers in age-related dementias

The identification of diagnostic-prognostic biomarkers of dementia has become a global priority due to the prevalence of neurodegenerative diseases in aging populations. The objective of this study was to assess the diagnostic performance of cerebrospinal fluid (CSF) biomarkers across patients affected by either Alzheimer’s disease (AD), tauopathies other than AD (TP), or vascular dementia (VD), and cognitively normal subjects (CNS). One hundred fifty-three patients were recruited and tested for classical AD CSF biomarkers- Amyloid-ß42 and tau proteins - and novel candidate biomarkers - neurofilament (NF-) light and microRNA (miR) -21, -125b, -146a, and -222.

All dementia patients had significantly higher concentrations of NF-light compared to CNS, with the TP group displaying the highest NF-light values. A significant inverse correlation was also observed between NF-light and cognitive impairment. Of the four miRNAs analyzed, miR-222 levels were significantly increased in VD patients compared to both CNS and AD. In addition, while NF-light showed a better diagnostic performance than miR-222 and classical AD biomarkers in differentiating TP and VD from CNS, classical AD biomarkers revealed higher performance in discriminating AD from non-AD disorders.

Overall, our results suggest that CSF NF-light and miR-222 are promising biomarkers that may help to diagnose non-AD disorders.

Global Brain Transcriptome Analysis of a Tpp1 Neuronal Ceroid Lipofuscinoses Mouse Model

In humans, homozygous mutations in the TPP1 gene results in loss of tripeptidyl peptidase 1 (TPP1) enzymatic activity, leading to late infantile neuronal ceroid lipofuscinoses disease. Using a mouse model that targets the Tpp1 gene and recapitulates the pathology and clinical features of the human disease, we analyzed end-stage (4 months) transcriptional changes associated with lack of TPP1 activity. Using RNA sequencing technology, Tpp1 expression changes in the forebrain/midbrain and cerebellum of 4-month-old homozygotes were compared with strain-related controls. Transcriptional changes were found in 510 and 1,550 gene transcripts in forebrain/midbrain and cerebellum, respectively, from Tpp1-deficient brain tissues when compared with age-matched controls. Analysis of the differentially expressed genes using the Ingenuity™ pathway software, revealed increased neuroinflammation activity in microglia and astrocytes that could lead to neuronal dysfunction, particularly in the cerebellum. We also observed upregulation in the production of nitric oxide and reactive oxygen species; activation of leukocyte extravasation signals and complement pathways; and downregulation of major transcription factors involved in control of circadian rhythm. Several of these expression changes were confirmed by independent quantitative polymerase chain reaction and histological analysis by mRNA in situ hybridization, which allowed for an in-depth anatomical analysis of the pathology and provided independent confirmation of at least two of the major networks affected in this model. The identification of differentially expressed genes has revealed new lines of investigation for this complex disorder that may lead to novel therapeutic targets.

Betanin purification from red beetroots and evaluation of its anti-oxidant and anti-inflammatory activity on LPS-activated microglial cells

Microglial activation can release free radicals and various pro-inflammatory cytokines, which implicates the progress of a neurodegenerative disease. Therefore suppression of microglial activation can be an appropriate strategy for combating neurodegenerative diseases. Betanin is a red food dye that acts as free radical scavenger and can be a promising candidate for this purpose. In this study, purification of betanin from red beetroots was carried out by normal phase colum chromatography, yielding 500 mg of betanin from 100 g of red beetroot. The purified betanin was evaluated by TLC, UV-visible, HPLC, ESI-MASS, FT-IR spectroscopy. Investigation on the inhibitory effect of betanin on activated microglia was performed using primary microglial culture. The results showed that betanin significantly inhibited lipopolysaccharide induced microglial function including the production of nitric oxide free radicals, reactive oxygen species, tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and interleukin-1 beta (IL-1β). Moreover, betanin modulated mitochondrial membrane potential, lysosomal membrane permeabilization and adenosine triphosphate. We further investigated the interaction of betanin with TNF-α, IL-6 and Nitric oxide synthase (iNOS or NOS2) using in silico molecular docking analysis. The docking results demonstrated that betanin have significant negative binding energy against active sites of TNF-α, IL-6 and iNOS.

The role of TLR4/NF-κB signaling pathway in activated microglia of rats with chronic high intraocular pressure and vitro scratch injury-induced microglia

Glaucoma is a kind of blind-causing disease with structural damages of optic nerve and defection of visual field. It is believed that the death of retinal ganglion cell (RGC) is a consequential event of over-reactive immune orchestral cells such as microglia. Previous evidences in animal and clinical studies show the innate immunity plays a pivotal role in neuro-inflammation of glaucoma. Toll-like receptor 4 (TLR4) is expressed on microglia and mediates many neuroinflammatory diseases. We aimed to explore the impacts of high intraocular pressure (IOP) on rat microglia in retina and the regulation of TLR4/NF-κB signaling pathway in scratched microglia cells. In our study, we successfully established chronic high IOP rat model by episcleral vein cauterization (EVC) which behaved like the chronic glaucoma. Besides, we set up an in vitro scratch-induced injury model in rat microglia cells. We found the level of activated microglia cells were significantly increased in the retina of chronic high IOP groups. Moreover, the inhibition of TLR4/NF-κB signaling pathway suppressed the expression of TLR4 protein and mRNA levels of P50, IL-6 and TNF-α. Our original study provided a theoretical basis on targeting TLR4/NF-κB to suppress pro-inflammatory factors releasing in activated microglia and it might be a good treatment target to prevent glaucoma from progressing.

TLR2 antagonism attenuates the hippocampal neuronal damage in a murine model of sleep apnea via inhibiting neuroinflammation and oxidative stress

BACKGROUND

Obstructive sleep apnea (OSA) in humans chronically promotes the neuronal damage in the hippocampus. Toll-like receptor 2 (TLR2) is pivotal for the development of numerous hippocampal diseases. Chronic intermittent hypoxia (CIH) is a prominent feature of OSA. Here in our study, the effects of TLR2 antagonism on the neural damage elicited by CIH were examined.

METHODS

Ortho-vanillin (O-vanillin) is an inhibitor of TLR2. Adult male mice were subjected to 8 h of intermittent hypoxia per day with or without O-vanillin for 28 days. Neuronal damage, the number of microglia, the interaction of TLR2 with its adapter protein myeloid differentiation factor 88 (MYD88), the expressions of inflammatory cytokines, and the oxidative stress were observed.

RESULTS

O-vanillin inhibited the increased interaction of TLR2 and MyD88, the activation of NFκB, the aggregation of microglia, the overexpression of proinflammatory agents, the elevation of oxidative stress, and hippocampal neuron cell apoptosis induced by CIH.

CONCLUSIONS

Our experiments indicate that TLR2 antagonism may alleviate the hippocampal neuronal damage caused by CIH via inhibiting neuroinflammation and oxidative stress.

Phagocytosis: Phenotypically Simple Yet a Mechanistically Complex Process

Phagocytosis is a pivotal immunological process, and its discovery by Elia Metchnikoff in 1882 was a step toward the establishment of the innate immune system as a separate branch of immunology. Elia Metchnikoff received the Nobel Prize in physiology and medicine for this discovery in 1908. Since its discovery almost 140 years before, phagocytosis remains the hot topic of research in immunology. The phagocytosis research has seen a great advancement since its first discovery. Functionally, phagocytosis is a simple immunological process required to engulf and remove pathogens, dead cells and tumor cells to maintain the immune homeostasis. However, mechanistically, it is a very complex process involving different mechanisms, induced and regulated by several pattern recognition receptors, soluble pattern recognition molecules, scavenger receptors (SRs) and opsonins. These mechanisms involve the formation of phagosomes, their maturation into phagolysosomes causing pathogen destruction or antigen synthesis to present them to major histocompatibility complex molecules for activating an adaptive immune response. Any defect in this mechanism may predispose the host to certain infections and inflammatory diseases (autoinflammatory and autoimmune diseases) along with immunodeficiency. The article is designed to discuss its mechanistic complexity at each level, varying from phagocytosis induction to phagolysosome resolution.

The gut microbiome in Parkinson's disease: A culprit or a bystander?

In recent years, large-scale metagenomics projects such as the Human Microbiome Project placed the gut microbiota under the spotlight of research on its role in health and in the pathogenesis several diseases, as it can be a target for novel therapeutical approaches. The emerging concept of a microbiota modulation of the gut-brain axis in the pathogenesis of neurodegenerative disorders has been explored in several studies in animal models, as well as in human subjects. Particularly, research on changes in the composition of gut microbiota as a potential trigger for alpha-synuclein (α-syn) pathology in Parkinson's disease (PD) has gained increasing interest. In the present review, we first provide the basis to the understanding of the role of gut microbiota in healthy subjects and the molecular basis of the gut-brain interaction, focusing on metabolic and neuroinflammatory factors that could trigger the alpha-synuclein conformational changes and aggregation. Then, we critically explored preclinical and clinical studies reporting on the changes in gut microbiota in PD, as compared to healthy subjects. Furthermore, we examined the relationship between the gut microbiota and PD clinical features, discussing data consistently reported across studies, as well as the potential sources of inconsistencies. As a further step toward understanding the effects of gut microbiota on PD, we discussed the relationship between dysbiosis and response to dopamine replacement therapy, focusing on Levodopa metabolism. We conclude that further studies are needed to determine whether the gut microbiota changes observed so far in PD patients is the cause or, instead, it is merely a consequence of lifestyle changes associated with the disease. Regardless, studies so far strongly suggest that changes in microbiota appears to be impactful in pathogenesis of neuroinflammation. Thus, dysbiotic microbiota in PD could influence the disease course and response to medication, especially Levodopa. Future research will assess the impact of microbiota-directed therapeutic intervention in PD patients.

Immunomodulatory role of the extracellular matrix protein tenascin-C in neuroinflammation

The extracellular matrix (ECM) consists of a dynamic network of various macromolecules that are synthesized and released by surrounding cells into the intercellular space. Glycoproteins, proteoglycans and fibrillar proteins are main components of the ECM. In addition to general functions such as structure and stability, the ECM controls several cellular signaling pathways. In this context, ECM molecules have a profound influence on intracellular signaling as receptor-, adhesion- and adaptor-proteins. Due to its various functions, the ECM is essential in the healthy organism, but also under pathological conditions. ECM constituents are part of the glial scar, which is formed in several neurodegenerative diseases that are accompanied by the activation and infiltration of glia as well as immune cells. Remodeling of the ECM modulates the release of pro- and anti-inflammatory cytokines affecting the fate of immune, glial and neuronal cells. Tenascin-C is an ECM glycoprotein that is expressed during embryonic central nervous system (CNS) development. In adults it is present at lower levels but reappears under pathological conditions such as in brain tumors, following injury and in neurodegenerative disorders and is highly associated with glial reactivity as well as scar formation. As a key modulator of the immune response during neurodegeneration in the CNS, tenascin-C is highlighted in this mini-review.

A Toll-receptor map underlies structural brain plasticity

Experience alters brain structure, but the underlying mechanism remained unknown. Structural plasticity reveals that brain function is encoded in generative changes to cells that compete with destructive processes driving neurodegeneration. At an adult critical period, experience increases fiber number and brain size in Drosophila. Here, we asked if Toll receptors are involved. Tolls demarcate a map of brain anatomical domains. Focusing on Toll-2, loss of function caused apoptosis, neurite atrophy and impaired behaviour. Toll-2 gain of function and neuronal activity at the critical period increased cell number. Toll-2 induced cycling of adult progenitor cells via a novel pathway, that antagonized MyD88-dependent quiescence, and engaged Weckle and Yorkie downstream. Constant knock-down of multiple Tolls synergistically reduced brain size. Conditional over-expression of Toll-2 and wek at the adult critical period increased brain size. Through their topographic distribution, Toll receptors regulate neuronal number and brain size, modulating structural plasticity in the adult brain.

Everything that you experience leaves its mark on your brain. When you learn something new, the neurons involved in the learning episode grow new projections and form new connections. Your brain may even produce new neurons. Physical exercise can induce similar changes, as can taking antidepressants. By contrast, stress, depression, ageing and disease can have the opposite effect, triggering neurons to break down and even die. The ability of the brain to change in response to experience is known as structural plasticity, and it is in a tug-of-war with processes that drive neurodegeneration.

Structural plasticity occurs in other species too: for example, it was described in the fruit fly more than a quarter of a century ago. Yet, the molecular mechanisms underlying structural plasticity remain unclear. Li et al. now show that, in fruit flies, this plasticity involves Toll receptors, a family of proteins present in the brain but best known for their role in the immune system.

Fruit flies have nine different Toll receptors, the most abundant being Toll-2. When activated, these proteins can trigger a series of molecular events in a cell. Li et al. show that increasing the amount of Toll-2 in the fly brain makes the brain produce new neurons. Activating neurons in a brain region has the same effect, and this increase in neuron number also depends on Toll-2. By contrast, reducing the amount of Toll-2 causes neurons to lose their projections and connections, and to die, and impairs fly behaviour.

Li et al. also show that each Toll receptor has a unique distribution across the fly brain. Different types of experiences activate different brain regions, and therefore different Toll receptors. These go on to trigger a common molecular cascade, but they modulate it such as to result in distinct outcomes. By working together in different combinations, Toll receptors can promote either the death or survival of neurons, and they can also drive specific brain cells to remain dormant or to produce new neurons.

By revealing how experience changes the brain, Li et al. provide clues to the way neurons work and form; these findings may also help to find new treatments for disorders that change brain structure, such as certain psychiatric conditions. Toll-like receptors in humans could thus represent a promising new target for drug discovery.

Synaptic Pruning by Microglia in Epilepsy

Structural and functional collapse of the balance between excitatory (E) and inhibitory (I) synapses, i.e., synaptic E/I balance, underlies the pathogeneses of various central nervous system (CNS) disorders. In epilepsy, the synaptic E/I balance tips toward excitation; thus, most of the existing epileptic remedies have focused on how to directly suppress the activity of neurons. However, because as many as 30% of patients with epilepsy are drug resistant, the discovery of new therapeutic targets is strongly desired. Recently, the roles of glial cells in epilepsy have gained attention because glial cells manipulate synaptic structures and functions in addition to supporting neuronal survival and growth. Among glial cells, microglia, which are brain-resident immune cells, have been shown to mediate inflammation, neuronal death and aberrant neurogenesis after epileptic seizures. However, few studies have investigated the involvement of synaptic pruning—one of the most important roles of microglia—in the epileptic brain. In this review, we propose and discuss the hypothesis that synaptic pruning by microglia is enhanced in the epileptic brain, drawing upon the findings of previous studies. We further discuss the possibility that aberrant synaptic pruning by microglia induces synaptic E/I imbalance, promoting the development and aggravation of epilepsy.

Higher soluble CD14 levels are associated with lower visuospatial memory performance in youth with HIV

OBJECTIVE

HIV-associated neurocognitive disorders persist despite early antiretroviral therapy (ART) and optimal viral suppression. We examined the relationship between immunopathogenesis driven by various pathways of immune activation and discrete neurocognitive performance domains in youth with HIV (YWH).

DESIGN

Observational cross-sectional study.

METHODS

YWH, ages 20-28 years, enrolled in Adolescent Medicine Trials Network 071/101 were assessed for biomarkers of macrophage, lymphocyte activation, and vascular inflammation using ELISA/multiplex assays. Standardized neurocognitive tests were performed, and demographically adjusted z-scores were combined to form indices of attention, motor, executive function, verbal, and visuospatial memory. Cross-sectional analysis of the relationship between 18 plasma inflammatory biomarkers and each neurocognitive domain was performed. Linear regression models were fit for each combination of log-transformed biomarker value and neurocognitive domain score, and were adjusted for demographics, socioeconomic status, substance use, depression, CD4 T-cell count, HIV viral load, and ART status.

RESULTS

Study included 128 YWH [mean age 23.8 (SD 1.7) years, 86% men, 68% African American]. Verbal and visuospatial memory domains were most significantly impaired in the cohort (z = -1.59 and -1.0, respectively). Higher sCD14 was associated with impaired visuospatial memory, which remained robust after adjusting for other biomarkers, demographics, and HIV-associated covariates. Among biomarkers of vascular inflammation, sICAM-1 was negatively associated with verbal memory and attention, whereas sVCAM-1 was positively associated with executive function and visuospatial memory. Specific neurocognitive domains were not associated with sCD163, LPS, or CCL2 levels.

CONCLUSION

Impaired visuospatial memory in YWH is associated with immune activation, as reflected by higher sCD14.

The role of innate immune responses and neuroinflammation in amyloid accumulation and progression of Alzheimer's disease

Alzheimer's disease (AD) is characterized by amyloid beta (Aβ) accumulation, tau pathology and neuroinflammation. Recently, there has been considerable interest in the role of neuroinflammation in directly contributing to the progression of AD. Studies in mice and humans have identified a role for microglial cells, the resident innate immune cells of the central nervous system, in AD. Activated microglia are a key hallmark of the disease and the secretion of proinflammatory cytokines by microglia may result in a positive feedback loop between neurons and microglia, resulting in ongoing low-grade inflammation. Traditionally, the pathways of Aβ production and neuroinflammation have been considered independently; however, recent studies suggest that these processes may converge to promote the pathology associated with AD. Here we review the importance of inflammation and microglia in AD development and effects of inflammatory responses on cellular pathways of neurons, including Aβ generation.

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.

Double deficiency of toll-like receptors 2 and 4 alters long-term neurological sequelae in mice cured of pneumococcal meningitis

Toll-like receptor (TLR) 2 and 4 signalling pathways are central to the body’s defence against invading pathogens during pneumococcal meningitis. Whereas several studies support their importance in innate immunity, thereby preventing host mortality, any role in protecting neurological function during meningeal infection is ill-understood. Here we investigated both the acute immunological reaction and the long-term neurobehavioural consequences of experimental pneumococcal meningitis in mice lacking both TLR2 and TLR4. The absence of these TLRs significantly impaired survival in mice inoculated intracerebroventricularly with Streptococcus pneumoniae. During the acute phase of infection, TLR2/4-deficient mice had lower cerebrospinal fluid concentrations of interleukin-1β, and higher interferon-γ, than their wild-type counterparts. After antibiotic cure, TLR2/4 double deficiency was associated with aggravation of behavioural impairment in mice, as shown by diurnal hypolocomotion throughout the adaptation phases in the Intellicage of TLR-deficient mice compared to their wild-type counterparts. While TLR2/4 double deficiency did not affect the cognitive ability of mice in a patrolling task, it aggravated the impairment of cognitive flexibility. We conclude that TLR2 and TLR4 are central to regulating the host inflammatory response in pneumococcal meningitis, which may mediate diverse compensatory mechanisms that protect the host not only against mortality but also long-term neurological complications.

Reformulating Pro-Oxidant Microglia in Neurodegeneration

In neurodegenerative diseases, microglia-mediated neuroinflammation and oxidative stress are central events. Recent genome-wide transcriptomic analyses of microglial cells under different disease conditions have uncovered a new subpopulation named disease-associated microglia (DAM). These studies have challenged the classical view of the microglia polarization state's proinflammatory M1 (classical activation) and immunosuppressive M2 (alternative activation). Molecular signatures of DAM and proinflammatory microglia (highly pro-oxidant) have shown clear differences, yet a partial overlapping gene profile is evident between both phenotypes. The switch activation of homeostatic microglia into reactive microglia relies on the selective activation of key surface receptors involved in the maintenance of brain homeostasis (a.k.a. pattern recognition receptors, PRRs). Two relevant PRRs are toll-like receptors (TLRs) and triggering receptors expressed on myeloid cells-2 (TREM2), whose selective activation is believed to generate either a proinflammatory or a DAM phenotype, respectively. However, the recent identification of endogenous disease-related ligands, which bind to and activate both TLRs and TREM2, anticipates the existence of rather complex microglia responses. Examples of potential endogenous dual ligands include amyloid β, galectin-3, and apolipoprotein E. These pleiotropic ligands induce a microglia polarization that is more complicated than initially expected, suggesting the possibility that different microglia subtypes may coexist. This review highlights the main microglia polarization states under disease conditions and their leading role orchestrating oxidative stress.

Dexamethasone exhibits its anti-inflammatory effects in S. aureus induced microglial inflammation via modulating TLR-2 and glucocorticoid receptor expression

Microglial inflammation plays crucial role in the pathogenesis of CNS infections including brain abscesses. Staphylococcus aureus (S. aureus) is considered as one of the major causative agents of brain abscesses. Due to the emergence of multidrug resistant bacteria the available treatment options including conventional antibiotics and steroid therapy become ineffective in terms of inflammation regulation which warrants further investigation to resolve this health issue. Microglial TLR-2 plays important roles in the bacterial recognition as well as induction of inflammation whereas glucocorticoid receptor (GR) triggers anti-inflammatory pathways in presence of glucocorticoids (GCs). The main objective of this study was to figure out the interdependency between TLR-2 and GR in presence of exogenous dexamethasone during microglial inflammation as an alternative therapeutic approach. Experiments were done either in TLR-2 neutralized condition or GR blocked condition in presence of dexamethasone. Free radicals production, arginase, superoxide dismutase (SOD), catalase enzyme activities and corticosterone concentration were measured along with Western blot analysis of TLR-2, GR and other inflammatory molecules. The results suggested that dexamethasone pre-treatment in TLR-2 neutralized condition efficiently reduces the inflammatory consequences of S. aureus induced microglial inflammation through up regulating GR expression. During TLR-2 blocking dexamethasone exerted its potent anti-inflammatory activities via suppressing reactive oxygen species (ROS), NO production and up regulating arginase, SOD and catalase activities at the time point of 90 min. Further in-vivo experiments are needed to conclude that dexamethasone could resolve brain inflammation possibly through microglial phenotypic switching from pro-inflammatory M1 to anti-inflammatory M2.

Blood-brain barrier and innate immunity in the pathogenesis of Alzheimer's disease

The pathogenesis of Alzheimer's disease (AD) is only partly understood. This is the probable reason why significant efforts to treat or prevent AD have been unsuccessful. In fact, as of April 2019, there have been 2094 studies registered for AD on the clinicaltrials.gov U.S. National Library of Science web page, of which only a few are still ongoing. In AD, abnormal accumulation of amyloid and tau proteins in the brain are thought to begin 10-20 years before the onset of overt symptoms, suggesting that interventions designed to prevent pathological amyloid and tau accumulation may be more effective than attempting to reverse a pathology once it is established. However, to be successful, such early interventions need to be selectively administered to individuals who will likely develop the disease long before the symptoms occur. Therefore, it is critical to identify early biomarkers that are strongly predictive of AD. Currently, patients are diagnosed on the basis of a variety of clinical scales, neuropsychological tests, imaging and laboratory modalities, but definitive diagnosis can be made only by postmortem assessment of underlying neuropathology. People suffering from AD thus may be misdiagnosed clinically with other primary causes of dementia, and vice versa, thereby also reducing the power of clinical trials. The amyloid cascade hypothesis fits well for the familial cases of AD with known mutations, but is not sufficient to explain sporadic, late-onset AD (LOAD) that accounts for over 95% of all cases. Since the earliest descriptions of AD there have been neuropathological features described other than amyloid plaques (AP) and neurofibrillary tangles (NFT), most notably gliosis and neuroinflammation. However, it is only recently that genetic and experimental studies have implicated microglial dysfunction as a causal factor for AD, as opposed to a merely biological response of its accumulation around AP. Additionally, many studies have suggested the importance of changes in blood-brain barrier (BBB) permeability in the pathogenesis of AD. Here we suggest how these less investigated aspects of the disease that have gained increased attention in recent years may contribute mechanistically to the development of lesions and symptoms of AD.

Lipopolysaccharide-Induced Neuroinflammation as a Bridge to Understand Neurodegeneration

A large body of experimental evidence suggests that neuroinflammation is a key pathological event triggering and perpetuating the neurodegenerative process associated with many neurological diseases. Therefore, different stimuli, such as lipopolysaccharide (LPS), are used to model neuroinflammation associated with neurodegeneration. By acting at its receptors, LPS activates various intracellular molecules, which alter the expression of a plethora of inflammatory mediators. These factors, in turn, initiate or contribute to the development of neurodegenerative processes. Therefore, LPS is an important tool for the study of neuroinflammation associated with neurodegenerative diseases. However, the serotype, route of administration, and number of injections of this toxin induce varied pathological responses. Thus, here, we review the use of LPS in various models of neurodegeneration as well as discuss the neuroinflammatory mechanisms induced by this toxin that could underpin the pathological events linked to the neurodegenerative process.

Constipation Increases Disability and Decreases Dopamine Levels in the Nigrostriatal System through Gastric Inflammatory Factors in Parkinson's Disease

OBJECTIVE

Recent studies suggest that not only is constipation a clinical marker of premotor phase in Parkinson's Disease (PD), but is also correlated with the duration and severity. Some reports indicated that inflammatory from gut dysbiosis might be involved in the pathogenesis of PD, but the correlation between them remains poorly understood. This study aims to investigate how the presence of constipation affects the dopamine level of nigrostriatal system and whether gastrointestinal (GI) inflammation is involved in the brain-gut axis.

METHODS

Clinical materials, serum inflammatory factors, and datum of dopamine level including 84 cases and 83 controls, were collected consecutively and randomly from November 1, 2017 to October 31, 2018. Dopamine levels of nigrostriatal system were detected by [18F]-DTBZ radiotracer (18F-AV-133). Data analysis was conducted by variance, covariance analysis, bicorrelation, partial correlation, chi-square analysis and logistic regression.

RESULTS

The mean age of cases was older than that of controls, and male predominance was also observed (P<0.05). The mean scores of Hoehn-Yahr and unified Parkinson's disease rating scale Ⅲ (UPDRS-Ⅲ) were of significantly different duration between two groups (P<0.05). The total dose of levodopa was not different between two groups (P>0.05). The dopamine levels of putamen and caudate nucleus, especially in the dorsal part of putamen, were significantly decreased in cases than that in controls (P<0.05). There were significant differences of complement 3 (C3) and complement 4 (C4) between cases and controls (P<0.05). Dopamine levels in putamen and caudate nucleus were negatively correlated with serum concentrations of immunoglobulin A (IgA), immunoglobulin G (IgG) and C3 in cases (P<0.05). But we did not observe similar negative correlations in controls (P>0.05).

CONCLUSION

The presence of constipation may increase the severity of motor symptoms and decrease dopamine levels of nigrostriatal system in PD. Inflammatory factors may be involved in the brain-gut axis of PD.