Rusty Microglia: Trainers of Innate Immunity in Alzheimer's Disease

[Uric acid, cognitive disorders, neurodegeneration]

This article examines the role of uric acid (UA) in cognitive changes and neurodegeneration, focusing on its functions as an antioxidant and prooxidant. Research suggests that changes in serum UA levels may be associated with the development or delay of cognitive impairment, especially in the context of neurodegenerative diseases such as Alzheimer's disease. It was revealed that there is a relationship between the level of UA and the dynamics of cognitive functions, indicating the potential neuroprotective properties of UA. Particular attention is paid to the balance between the antioxidant and prooxidant properties of UA, which may play a key role in protecting neurons from damage. However, research results are not clear-cut, highlighting the need for further research to more fully understand the role of UA in cognitive processes. Determining the optimal serum UA level may be an important step in developing strategies for the prevention and treatment of cognitive impairment associated with neurodegeneration. Overall, these studies advance the understanding of the mechanisms underlying the interaction between uric acid metabolism and brain health.

Exploring Potential Mechanisms Accounting for Iron Accumulation in the Central Nervous System of Patients with Alzheimer's Disease

Elevated levels of iron occur in both cortical and subcortical regions of the CNS in patients with Alzheimer's disease. This accumulation is present early in the disease process as well as in more advanced stages. The factors potentially accounting for this increase are numerous, including: (1) Cells increase their uptake of iron and reduce their export of iron, as iron becomes sequestered (trapped within the lysosome, bound to amyloid β or tau, etc.); (2) metabolic disturbances, such as insulin resistance and mitochondrial dysfunction, disrupt cellular iron homeostasis; (3) inflammation, glutamate excitotoxicity, or other pathological disturbances (loss of neuronal interconnections, soluble amyloid β, etc.) trigger cells to acquire iron; and (4) following neurodegeneration, iron becomes trapped within microglia. Some of these mechanisms are also present in other neurological disorders and can also begin early in the disease course, indicating that iron accumulation is a relatively common event in neurological conditions. In response to pathogenic processes, the directed cellular efforts that contribute to iron buildup reflect the importance of correcting a functional iron deficiency to support essential biochemical processes. In other words, cells prioritize correcting an insufficiency of available iron while tolerating deposited iron. An analysis of the mechanisms accounting for iron accumulation in Alzheimer's disease, and in other relevant neurological conditions, is put forward.

Microglial-specific knockdown of iron import gene, Slc11a2, blunts LPS-induced neuroinflammatory responses in a sex-specific manner

Neuroinflammation and microglial iron load are significant hallmarks found in several neurodegenerative diseases. In in vitro systems, microglia preferentially upregulate the iron importer, divalent metal transporter 1 (DMT1, gene name Slc11a2) in response to inflammatory stimuli, and it has been shown that iron can augment cellular inflammation, suggesting a feed-forward loop between mechanisms involved in iron import and inflammatory signaling. However, it is not understood how microglial iron import mechanisms contribute to inflammation in vivo, or whether altering a microglial iron-related gene affects the inflammatory response. These studies aimed to determine the effect of knocking down microglial iron import gene Slc11a2 on the inflammatory response in vivo. We generated a novel model of tamoxifen-inducible, microglial-specific Slc11a2 knockdown using Cx3cr1Cre-ERT2 mice. Transgenic male and female mice were administered intraperitoneal saline or lipopolysaccharide (LPS) and assessed for sickness behavior post-injection. Plasma cytokines and microglial bulk RNA sequencing (RNASeq) analyses were performed at 4 h post-LPS, and microglia were collected for gene expression analysis after 24 h. A subset of mice was assessed in a behavioral test battery following LPS-induced sickness recovery. Control male, but not female, mice significantly upregulated microglial Slc11a2 at 4 and 24 h following LPS. In Slc11a2 knockdown mice, we observed an improvement in the acute behavioral sickness response post-LPS in male, but not female, animals. Microglia from male, but not female, knockdown animals exhibited a significant decrease in LPS-provoked pro-inflammatory cytokine expression after 24 h. RNASeq data from male knockdown microglia 4 h post-LPS revealed a robust downregulation in inflammatory genes including Il6, Tnfα, and Il1β, and an increase in anti-inflammatory and homeostatic markers (e.g., Tgfbr1, Cx3cr1, and Trem2). This corresponded with a profound decrease in plasma pro-inflammatory cytokines 4 h post-LPS. At 4 h, male knockdown microglia also upregulated expression of markers of iron export, iron recycling, and iron homeostasis and decreased iron storage and import genes, along with pro-oxidant markers such as Cybb, Nos2, and Hif1α. Overall, this work elucidates how manipulating a specific gene involved in iron import in microglia alters acute inflammatory signaling and overall cell activation state in male mice. These data highlight a sex-specific link between a microglial iron import gene and the pro-inflammatory response to LPS in vivo, providing further insight into the mechanisms driving neuroinflammatory disease.

Investigating the Synergistic Potential of Low-Dose HDAC3 Inhibition and Radiotherapy in Alzheimer's Disease Models

We have previously shown that histone deacetylase (HDAC) inhibition and cranial radiotherapy (RT) independently improve molecular and behavioral Alzheimer's disease (AD)-like phenotypes. In the present study, we investigate the synergistic potential of using both RT and HDACi as a low-dose combination therapy (LDCT) to maximize disease modification (reduce neuroinflammation and amyloidogenic APP processing, increase neurotrophic gene expression) while minimizing the potential for treatment-associated side effects.LDCT consisted of daily administration of the HDAC3 inhibitor RGFP966 and/or bi-weekly cranial x-irradiation. Amyloid-beta precursor protein (APP) processing and innate immune response to LDCT were assessed in vitro and in vivo using human and murine cell models and 3xTg-AD mice. After 2 months of LDCT in mice, behavioral analyses as well as expression and modification of key AD-related targets (Aβ, tau, Csf1r, Bdnf, etc.) were assessed in the hippocampus (HIP) and prefrontal cortex (PFC).LDCT induced a tolerant, anti-inflammatory innate immune response in microglia and increased non-amyloidogenic APP processing in vitro. Both RT and LDCT improved the rate of learning and spatial memory in the Barnes maze test. LDCT induced a unique anti-AD HIP gene expression profile that included upregulation of neurotrophic genes and downregulation of inflammation-related genes. RT lowered HIP Aβ42/40 ratio and Bace1 protein, while LDCT lowered PFC p-tau181 and HIP Bace1 levels.Our study supports the rationale for combining complementary therapeutic approaches at low doses to target multifactorial AD pathology synergistically. Namely, LDCT with RGFP966 and cranial RT shows disease-modifying potential against a wide range of AD-related hallmarks.

Contemporary Antiretroviral Therapy Dysregulates Iron Transport and Augments Mitochondrial Dysfunction in HIV-Infected Human Microglia and Neural-Lineage Cells

HIV-associated cognitive dysfunction during combination antiretroviral therapy (cART) involves mitochondrial dysfunction, but the impact of contemporary cART on chronic metabolic changes in the brain and in latent HIV infection is unclear. We interrogated mitochondrial function in a human microglia (hμglia) cell line harboring inducible HIV provirus and in SH-SY5Y cells after exposure to individual antiretroviral drugs or cART, using the MitoStress assay. cART-induced changes in protein expression, reactive oxygen species (ROS) production, mitochondrial DNA copy number, and cellular iron were also explored. Finally, we evaluated the ability of ROS scavengers or plasmid-mediated overexpression of the antioxidant iron-binding protein, Fth1, to reverse mitochondrial defects. Contemporary antiretroviral drugs, particularly bictegravir, depressed multiple facets of mitochondrial function by 20-30%, with the most pronounced effects in latently infected HIV+ hμglia and SH-SY5Y cells. Latently HIV-infected hμglia exhibited upregulated glycolysis. Increases in total and/or mitochondrial ROS, mitochondrial DNA copy number, and cellular iron accompanied mitochondrial defects in hμglia and SH-SY5Y cells. In SH-SY5Y cells, cART reduced mitochondrial iron-sulfur-cluster-containing supercomplex and subunit expression and increased Nox2 expression. Fth1 overexpression or pre-treatment with N-acetylcysteine prevented cART-induced mitochondrial dysfunction. Contemporary cART impairs mitochondrial bioenergetics in hμglia and SH-SY5Y cells, partly through cellular iron accumulation; some effects differ by HIV latency.

Training vs. Tolerance: The Yin/Yang of the Innate Immune System

For almost nearly a century, memory functions have been attributed only to acquired immune cells. Lately, this paradigm has been challenged by an increasing number of studies revealing that innate immune cells are capable of exhibiting memory-like features resulting in increased responsiveness to subsequent challenges, a process known as trained immunity (known also as innate memory). In contrast, the refractory state of endotoxin tolerance has been defined as an immunosuppressive state of myeloid cells portrayed by a significant reduction in the inflammatory capacity. Both training as well tolerance as adaptive features are reported to be accompanied by epigenetic and metabolic alterations occurring in cells. While training conveys proper protection against secondary infections, the induction of endotoxin tolerance promotes repairing mechanisms in the cells. Consequently, the inappropriate induction of these adaptive cues may trigger maladaptive effects, promoting an increased susceptibility to secondary infections—tolerance, or contribute to the progression of the inflammatory disorder—trained immunity. This review aims at the discussion of these opposing manners of innate immune and non-immune cells, describing the molecular, metabolic and epigenetic mechanisms involved and interpreting the clinical implications in various inflammatory pathologies.

Neurodegeneration and astrogliosis in the entorhinal cortex in Alzheimer's disease: Stereological layer-specific assessment and proteomic analysis

INTRODUCTION

The entorhinal cortex is among the earliest areas involved in Alzheimer's disease. Volume reduction and neural loss in this area have been widely reported. Human entorhinal cortex atrophy is, in part, due to neural loss, but microglial and/or astroglial involvement in the different layers remains unclear. Additionally, -omic approaches in the human entorhinal cortex are scarce.

METHODS

Herein, stereological layer-specific and proteomic analyses were carried out in the human brain.

RESULTS

Neurodegeneration, microglial reduction, and astrogliosis have been demonstrated, and proteomic data have revealed relationships with up- (S100A6, PPP1R1B, BAG3, and PRDX6) and downregulated (GSK3B, SYN1, DLG4, and RAB3A) proteins. Namely, clusters of these proteins were related to synaptic, neuroinflammatory, and oxidative stress processes.

DISCUSSION

Differential layer involvement among neural and glial populations determined by proteinopathies and identified proteins related to neurodegeneration and astrogliosis could explain how the cortical circuitry facilitates pathological spreading within the medial temporal lobe.

Role of Lipocalin-2 in Amyloid-Beta Oligomer-Induced Mouse Model of Alzheimer's Disease

Lipocalin-2 (LCN2) is an inflammatory protein with diverse functions in the brain. Although many studies have investigated the mechanism of LCN2 in brain injuries, the effect of LCN2 on amyloid-toxicity-related memory deficits in a mouse model of Alzheimer’s disease (AD) has been less studied. We investigated the role of LCN2 in human AD patients using a mouse model of AD. We created an AD mouse model by injecting amyloid-beta oligomer (AβO) into the hippocampus. In this model, animals exhibited impaired learning and memory. We found LCN2 upregulation in the human brain frontal lobe, as well as a positive correlation between white matter ischemic changes and serum LCN2. We also found increased astrocytic LCN2, microglia activation, iron accumulation, and blood–brain barrier disruption in AβO-treated hippocampi. These findings suggest that LCN2 is involved in a variety of amyloid toxicity mechanisms, especially neuroinflammation and oxidative stress.

Western diet as a trigger of Alzheimer's disease: From metabolic syndrome and systemic inflammation to neuroinflammation and neurodegeneration

An excess of saturated fatty acids and simple sugars in the diet is a known environmental risk factor of Alzheimer's disease (AD) but the holistic view of the interacting processes through which such diet may contribute to AD pathogenesis is missing. We addressed this need through extensive analysis of published studies investigating the effects of western diet (WD) on AD development in humans and laboratory animals. We reviewed WD-induced systemic alterations comprising metabolic changes, induction of obesity and adipose tissue inflammation, gut microbiota dysbiosis and acceleration of systemic low-grade inflammation. Next we provide an overview of the evidence demonstrating that WD-associated systemic alterations drive impairment of the blood-brain barrier (BBB) and development of neuroinflammation paralleled by accumulation of toxic amyloid. Later these changes are followed by dysfunction of synaptic transmission, neurodegeneration and finally memory and cognitive impairment. We conclude that WD can trigger AD by acceleration of inflammaging, and that BBB impairment induced by metabolic and systemic inflammation play the central role in this process. Moreover, the concurrence of neuroinflammation and Aβ dyshomeostasis, which by reciprocal interactions drive the vicious cycle of neurodegeneration, contradicts Aβ as the primary trigger of AD. Given that in 2019 the World Health Organization recommended focusing on modifiable risk factors in AD prevention, this overview of the sequential, complex pathomechanisms initiated by WD, which can lead from peripheral disturbances to neurodegeneration, can support future prevention strategies.

Research progress of hydrogen sulfide in Alzheimer's disease from laboratory to hospital: a narrative review

Alzheimer's disease is a neurodegenerative disease that mainly occurs in old age and early stages. Its main manifestations are memory impairment, aphasia, apraxia, loss of identity, abstract thinking and impairment of computing power, personality and behavior changes, etc. At present, the treatment of Alzheimer's disease only stays on reducing the disease and delaying the development, which is also a difficult problem to overcome in clinical practice. Hydrogen sulfide, as a third gaseous signal molecule after carbon monoxide and nitrogen monoxide, has become very popular in recent years. It shows very promising prospects in the Alzheimer's disease model. It can protect the nerve function and prevent the progress of the disease by affecting the amyloid precursor protein metabolism, anti-apoptosis, anti-inflammatory, and antioxidant pathways. Therefore, this article summarizes the relevant basic and clinical research of hydrogen sulfide in Alzheimer's disease, and discusses its progress and findings and mechanism characteristics.

The Role of Butyrylcholinesterase and Iron in the Regulation of Cholinergic Network and Cognitive Dysfunction in Alzheimer's Disease Pathogenesis

Alzheimer’s disease (AD), the most common form of dementia in elderly individuals, is marked by progressive neuron loss. Despite more than 100 years of research on AD, there is still no treatment to cure or prevent the disease. High levels of amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs) in the brain are neuropathological hallmarks of AD. However, based on postmortem analyses, up to 44% of individuals have been shown to have high Aβ deposits with no clinical signs, due to having a “cognitive reserve”. The biochemical mechanism explaining the prevention of cognitive impairment in the presence of Aβ plaques is still unknown. It seems that in addition to protein aggregation, neuroinflammatory changes associated with aging are present in AD brains that are correlated with a higher level of brain iron and oxidative stress. It has been shown that iron accumulates around amyloid plaques in AD mouse models and postmortem brain tissues of AD patients. Iron is required for essential brain functions, including oxidative metabolism, myelination, and neurotransmitter synthesis. However, an imbalance in brain iron homeostasis caused by aging underlies many neurodegenerative diseases. It has been proposed that high iron levels trigger an avalanche of events that push the progress of the disease, accelerating cognitive decline. Patients with increased amyloid plaques and iron are highly likely to develop dementia. Our observations indicate that the butyrylcholinesterase (BChE) level seems to be iron-dependent, and reports show that BChE produced by reactive astrocytes can make cognitive functions worse by accelerating the decay of acetylcholine in aging brains. Why, even when there is a genetic risk, do symptoms of the disease appear after many years? Here, we discuss the relationship between genetic factors, age-dependent iron tissue accumulation, and inflammation, focusing on AD.

Porphyromonas Gingivalis May Seek the Alzheimer's Disease Brain to Acquire Iron from Its Surplus

Iron accumulates in the brain of subjects with Alzheimer’s disease (AD). Here it promotes the aggregation of amyloid-β plaques in which it is abundant. Iron induces amyloid-β neurotoxicity by damaging free radicals and causing oxidative stress in brain areas with neurodegeneration. It can also bind to tau in AD and enhance the toxicity of tau through co-localization with neurofibrillary tangles and induce accumulation of these tangles. Porphyromonas gingivalis is a key oral pathogen in the widespread biofilm-induced disease “chronic” periodontitis, and recently, has been suggested to have an important role in the pathogenesis of AD. P. gingivalis has an obligate requirement for iron. The current paper suggests that P. gingivalis seeks the AD brain, where it has been identified, to satisfy this need. If this is correct, iron chelators binding iron could have beneficial effects in the treatment of AD. Indeed, studies from both animal AD models and humans with AD have indicated that iron chelators, e.g., lactoferrin, can have such effects. Lactoferrin can also inhibit P. gingivalis growth and proteinases and its ability to form biofilm.

Cholinergic Modulation of Glial Function During Aging and Chronic Neuroinflammation

Aging is a complex biological process that increases the risk of age-related cognitive degenerative diseases such as dementia, including Alzheimer’s disease (AD), Lewy Body Dementia (LBD), and mild cognitive impairment (MCI). Even non-pathological aging of the brain can involve chronic oxidative and inflammatory stress, which disrupts the communication and balance between the brain and the immune system. There has been an increasingly strong connection found between chronic neuroinflammation and impaired memory, especially in AD. While microglia and astrocytes, the resident immune cells of the central nervous system (CNS), exerting beneficial effects during the acute inflammatory phase, during chronic neuroinflammation they can become more detrimental. Central cholinergic circuits are involved in maintaining normal cognitive function and regulating signaling within the entire cerebral cortex. While neuronal-glial cholinergic signaling is anti-inflammatory and anti-oxidative, central cholinergic neuronal degeneration is implicated in impaired learning, memory sleep regulation, and attention. Although there is evidence of cholinergic involvement in memory, fewer studies have linked the cholinergic anti-inflammatory and anti-oxidant pathways to memory processes during development, normal aging, and disease states. This review will summarize the current knowledge of cholinergic effects on microglia and astroglia, and their role in both anti-inflammatory and anti-oxidant mechanisms, concerning normal aging and chronic neuroinflammation. We provided details on how stimulation of α7 nicotinic acetylcholine (α7nACh) receptors can be neuroprotective by increasing amyloid-β phagocytosis, decreasing inflammation and reducing oxidative stress by promoting the nuclear factor erythroid 2-related factor 2 (Nrf2) pathways and decreasing the release of pro-inflammatory cytokines. There is also evidence for astroglial α7nACh receptor stimulation mediating anti-inflammatory and antioxidant effects by inhibiting the nuclear factor-κB (NF-κB) pathway and activating the Nrf2 pathway respectively. We conclude that targeting cholinergic glial interactions between neurons and glial cells via α7nACh receptors could regulate neuroinflammation and oxidative stress, relevant to the treatment of several neurodegenerative diseases.

Dietary Wheat Amylase Trypsin Inhibitors Impact Alzheimer's Disease Pathology in 5xFAD Model Mice

Wheat amylase trypsin inhibitors (ATIs) represent a common dietary protein component of gluten-containing cereals (wheat, rye, and barley). They act as toll-like receptor 4 ligands, and are largely resistant to intestinal proteases, eliciting a mild inflammatory response within the intestine after oral ingestion. Importantly, nutritional ATIs exacerbated inflammatory bowel disease and features of fatty liver disease and the metabolic syndrome in mice. For Alzheimer’s disease (AD), both inflammation and altered insulin resistance are major contributing factors, impacting onset as well as progression of this devastating brain disorder in patients. In this study, we evaluated the impact of dietary ATIs on a well-known rodent model of AD (5xFAD). We assessed metabolic, behavioral, inflammatory, and microbial changes in mice consuming different dietary regimes with and without ATIs, consumed ad libitum for eight weeks. We demonstrate that ATIs, with or without a gluten matrix, had an impact on the metabolism and gut microbiota of 5xFAD mice, aggravating pathological hallmarks of AD. If these findings can be translated to patients, an ATI-depleted diet might offer an alternative therapeutic option for AD and warrants clinical intervention studies.

Antidepressive properties of macrophage-colony stimulating factor in a mouse model of depression induced by chronic unpredictable stress

Previous studies have reported that macrophage-colony stimulating factor (M-CSF), a drug that is used to treat hematological system disease, can ameliorate chronic stress-induced depressive-like behaviors in mice. This indicates that M-CSF could be developed into a novel antidepressant. Here, we investigated the antidepressive properties of M-CSF, aiming to explore its potential values in depression treatment. Our results showed that a single M-CSF injection at the dose of 75 and 100 μg/kg, but not at 25 or 50 μg/kg, ameliorated chronic unpredictable stress (CUS)-induced depressive-like behaviors in mice at 5 h after the drug treatment. In a time-dependent experiment, a single M-CSF injection (100 μg/kg) was found to ameliorate the CUS-induced depressive-like behaviors in mice at 5 and 8 h, but not at 3 h, after the drug treatment. The antidepressant effect of the single M-CSF injection (100 μg/kg) in chronically-stressed mice persisted at least 10 days and disappeared at 14 days after the drug treatment. Moreover, 14 days after the first injection, a second M-CSF injection (100 μg/kg) still produced antidepressant effects at 5 h after the drug treatment in chronically-stressed mice who re-displayed depressive-like phenotypes. The antidepressant effect of M-CSF appeared to be mediated by the activation of the hippocampal microglia, as pre-inhibition of microglia by minocycline (40 mg/kg) or PLX3397 (290 mg/kg) pretreatment prevented the antidepressant effect of M-CSF in CUS mice. These results demonstrate that M-CSF produces rapid and sustained antidepressant effects via the activation of the microglia in the hippocampus in a dose- and time-dependent manner.

Regulation of tissue iron homeostasis: the macrophage "ferrostat"

Iron is an essential element for multiple fundamental biological processes required for life; yet iron overload can be cytotoxic. Consequently, iron concentrations at the cellular and tissue level must be exquisitely governed by mechanisms that complement and fine-tune systemic control. It is well appreciated that macrophages are vital for systemic iron homeostasis, supplying or sequestering iron as needed for erythropoiesis or bacteriostasis, respectively. Indeed, recycling of iron through erythrophagocytosis by splenic macrophages is a major contributor to systemic iron homeostasis. However, accumulating evidence suggests that tissue-resident macrophages regulate local iron availability and modulate the tissue microenvironment, contributing to cellular and tissue function. Here, we summarize the significance of tissue-specific regulation of iron availability and highlight how resident macrophages are critical for this process. This tissue-dependent regulation has broad implications for understanding both resident macrophage function and tissue iron homeostasis in health and disease.

Associations between Monocyte and T Cell Cytokine Profiles in Autism Spectrum Disorders: Effects of Dysregulated Innate Immune Responses on Adaptive Responses to Recall Antigens in a Subset of ASD Children

Changes in monocyte cytokine production with toll like receptor (TLR) agonists in subjects with autism spectrum disorders (ASD) were best reflected by the IL-1β/IL-10 ratios in our previous research. The IL-1β/IL-10 based subgrouping (low, normal, and high) of ASD samples revealed marked differences in microRNA expression, and mitochondrial respiration. However, it is unknown whether the IL-1β/IL-10 ratio based subgrouping is associated with changes in T cell cytokine profiles or monocyte cytokine profiles with non-TLR agonists. In ASD (n = 152) and non-ASD (n = 41) subjects, cytokine production by peripheral blood monocytes (PBMo) with TLR agonists and β-glucan, an inflammasome agonist, and T cell cytokine production by peripheral blood mononuclear cells (PBMCs) with recall antigens (Ags) (food and candida Ags) were concurrently measured. Changes in monocyte cytokine profiles were observed with β-glucan in the IL-1β/IL-10 ratio based ASD subgroups, along with changes in T cell cytokine production and ASD subgroup-specific correlations between T cell and monocyte cytokine production. Non-ASD controls revealed considerably less of such correlations. Altered innate immune responses in a subset of ASD children are not restricted to TLR pathways and correlated with changes in T cell cytokine production. Altered trained immunity may play a role in the above described changes.

Potentiation of cannabinoid signaling in microglia by adenosine A2A receptor antagonists

Neuroprotective M2-skewed microglia appear as promising to alter the course of neurodegenerative diseases and G protein-coupled receptors (GPCRs) are potential targets to achieve such microglial polarization. A common feature of adenosine A_2A (A_2A R) and cannabinoid CB₂ (CB₂ R) GPCRs in microglia is that their expression is upregulated in Alzheimer's disease (AD). On the one hand, CB₂ R seems a target for neuroprotection, delaying neurodegenerative processes like those associated to AD or Parkinson's diseases. A_2A R antagonists reduce amyloid burden and improve cognitive performance and memory in AD animal models. We here show a close interrelationship between these two receptors in microglia; they are able to physically interact and affect the signaling of each other, likely due to conformational changes within the A_2A -CB₂ receptor heteromer (A_2A -CB₂ Het). Particularly relevant is the upregulation of A_2A -CB₂ Het expression in samples from the APP_Sw ,_Ind AD transgenic mice model. The most relevant finding, confirmed in both heterologous cells and in primary cultures of microglia, was that blockade of A_2A receptors results in increased CB₂ R-mediated signaling. This heteromer-specific feature suggests that A_2A R antagonists would potentiate, via microglia, the neuroprotective action of endocannabinoids with implications for AD therapy.

Down-Regulation of Essential Synaptic Components by GI-Tract Microbiome-Derived Lipopolysaccharide (LPS) in LPS-Treated Human Neuronal-Glial (HNG) Cells in Primary Culture: Relevance to Alzheimer's Disease (AD)

Trans-synaptic neurotransmission of both electrical and neurochemical information in the central nervous system (CNS) is achieved through a highly interactive network of neuron-specific synaptic proteins that include pre-synaptic and post-synaptic elements. These elements include a family of several well-characterized integral- and trans-membrane synaptic core proteins necessary for the efficient operation of this complex signaling network, and include the pre-synaptic proteins: (i) neurexin-1 (NRXN-1); (ii) the synaptosomal-associated phosphoprotein-25 (SNAP-25); (iii) the phosphoprotein synapsin-2 (SYN-2); and the post-synaptic elements: (iv) neuroligin (NLGN), a critical cell adhesion protein; and (v) the SH3-ankyrin repeat domain, proline-rich cytoskeletal scaffolding protein SHANK3. All five of these pre- and post-synaptic proteins have been found to be significantly down-regulated in primary human neuronal-glial (HNG) cell co-cultures after exposure to Bacteroides fragilis lipopolysaccharide (BF-LPS). Interestingly, LPS has also been reported to be abundant in Alzheimer's disease (AD) affected brain cells where there are significant deficits in this same family of synaptic components. This "Perspectives" paper will review current research progress and discuss the latest findings in this research area. Overall these experimental results provide evidence (i) that gastrointestinal (GI) tract-derived Gram-negative bacterial exudates such as BF-LPS express their neurotoxicity in the CNS in part through the directed down-regulation of neuron-specific neurofilaments and synaptic signaling proteins; and (ii) that this may explain the significant alterations in immune-responses and cognitive deficits observed after bacterial-derived LPS exposure to the human CNS.

Trained Innate Immunity Not Always Amicable

The concept of „trained innate immunity" is understood as the ability of innate immune cells to remember invading agents and to respond nonspecifically to reinfection with increased strength. Trained immunity is orchestrated by epigenetic modifications leading to changes in gene expression and cell physiology. Although this phenomenon was originally seen mainly as a beneficial effect, since it confers broad immunological protection, enhanced immune response of reprogrammed innate immune cells might result in the development or persistence of chronic metabolic, autoimmune or neuroinfalmmatory disorders. This paper overviews several examples where the induction of trained immunity may be essential in the development of diseases characterized by flawed innate immune response.