Dynamics of the Complement, Cytokine, and Chemokine Systems in the Regulation of Synaptic Function and Dysfunction Relevant to Alzheimer’s Disease

Effects of Cerebrospinal Fluids from Alzheimer and Non-Alzheimer Patients on Neurons-Astrocytes-Microglia Co-Culture

Alzheimer's disease (AD) is the most common form of dementia, characterized by the accumulation of β-amyloid plaques, tau tangles, neuroinflammation, and synaptic/neuronal loss, the latter being the strongest correlating factor with memory and cognitive impairment. Through an in vitro study on a neurons-astrocytes-microglia (NAM) co-culture system, we analyzed the effects of cerebrospinal fluid (CSF) samples from AD and non-AD patients (other neurodegenerative pathologies). Treatment with CSF from AD patients showed a loss of neurofilaments and spheroids, suggesting the presence of elements including CX3CL1 (soluble form), destabilizing the neurofilaments, cellular adhesion processes, and intercellular contacts. The NAM co-cultures were analyzed in immunofluorescence assays for several markers related to AD, such as through zymography, where the expression of proteolytic enzymes was quantified both in cell extracts and the co-cultures' conditioned medium (CM). Through qRT-PCR assays, several genes involved in the formation of β-amyloid plaque, in phosphorylation of tau, and in inflammation pathways and MMP expression were investigated.

Structure characterisation of polysaccharides purified from Boletus aereus Bull. and its improvement on AD-like behaviours via reliving neuroinflammation in APP/PS1 mice

The water-soluble neutral polysaccharide BEP2, with a molecular weight of 26.65 kDa, was isolated from the aqueous extract obtained from the fruiting bodies of Boletus aereus Bull. BEP2 primarily comprises Gal, with specific site substitutions speculated at partial positions, such as the substitution of -OCH3 at position H-3 or the branch at position C-2 including α-L-Fucp-(1→, α-D-Manp-(1 → and α-D-Manp-(1 → 3)-α-L-Fucp-(1 → 6)-β-D-Glcp-(1→. Treatment with BEP2 significantly enhanced learning, memory, and cognitive function, while concurrently reducing the accumulation of β-amyloid and suppressing neuroinflammation within the brains of APP/PS1 mice. Based on the results of biochemical detection, gut microbiota analysis, and metabolomic profiling, we found that BEP2 significantly upregulated the abundance of two bacterial families while downregulation that of seven bacterial families within the intestinal ecosystem. Notably, the abundance of the S24-7 family was significantly increased. Treatment with BEP2 upregulated five metabolites, while downregulating three metabolites, including norepinephrine. Additionally, BEP2 decreased the levels of interleukin (IL)-1β and IL-6, regulated the activities of microglial cells and astrocytes and increased the levels of the chemokine fractalkine (CX3CL1) and its receptor on microglia (CX3CR1), as well as that of transforming growth factor (TGF)-β1. These findings confirmed the suppressive effects of BEP2 on neuroinflammation.

The role of natural flavonoids on neuroinflammation as a therapeutic target for Alzheimer's disease: a narrative review

Alzheimer's disease is a neurodegenerative disease that affects a large proportion of older adult people and is characterized by memory loss, progressive cognitive impairment, and various behavioral disturbances. Although the pathological mechanisms underlying Alzheimer's disease are complex and remain unclear, previous research has identified two widely accepted pathological characteristics: extracellular neuritic plaques containing amyloid beta peptide, and intracellular neurofibrillary tangles containing tau. Furthermore, research has revealed the significant role played by neuroinflammation over recent years. The inflammatory microenvironment mainly consists of microglia, astrocytes, the complement system, chemokines, cytokines, and reactive oxygen intermediates; collectively, these factors can promote the pathological process and aggravate the severity of Alzheimer's disease. Therefore, the development of new drugs that can target neuroinflammation will be a significant step forward for the treatment of Alzheimer's disease. Flavonoids are plant-derived secondary metabolites that possess various bioactivities. Previous research found that multiple natural flavonoids could exert satisfactory treatment effects on the neuroinflammation associated with Alzheimer's disease. In this review, we describe the pathogenesis and neuroinflammatory processes of Alzheimer's disease, and summarize the effects and mechanisms of 13 natural flavonoids (apigenin, luteolin, naringenin, quercetin, morin, kaempferol, fisetin, isoquercitrin, astragalin, rutin, icariin, mangiferin, and anthocyanin) derived from plants or medicinal herbs on neuroinflammation in Alzheimer's disease. As an important resource for the development of novel compounds for the treatment of critical diseases, it is essential that we focus on the exploitation of natural products. In particular, it is vital that we investigate the effects of flavonoids on the neuroinflammation associated with Alzheimer's disease in greater detail.

Role of Blood-Brain Barrier Dysfunction in Delirium following Non-cardiac Surgery in Older Adults

OBJECTIVE

Although animal models suggest a role for blood-brain barrier dysfunction in postoperative delirium-like behavior, its role in postoperative delirium and postoperative recovery in humans is unclear. Thus, we evaluated the role of blood-brain barrier dysfunction in postoperative delirium and hospital length of stay among older surgery patients.

METHODS

Cognitive testing, delirium assessment, and cerebrospinal fluid and blood sampling were prospectively performed before and after non-cardiac, non-neurologic surgery. Blood-brain barrier dysfunction was assessed using the cerebrospinal fluid-to-plasma albumin ratio (CPAR).

RESULTS

Of 207 patients (median age = 68 years, 45% female) with complete CPAR and delirium data, 26 (12.6%) developed postoperative delirium. Overall, CPAR increased from before to 24 hours after surgery (median change = 0.28, interquartile range [IQR] = -0.48 to 1.24, Wilcoxon p = 0.001). Preoperative to 24 hours postoperative change in CPAR was greater among patients who developed delirium versus those who did not (median [IQR] = 1.31 [0.004 to 2.34] vs 0.19 [-0.55 to 1.08], p = 0.003). In a multivariable model adjusting for age, baseline cognition, and surgery type, preoperative to 24 hours postoperative change in CPAR was independently associated with delirium occurrence (per CPAR increase of 1, odds ratio = 1.30, 95% confidence interval [CI] = 1.03-1.63, p = 0.026) and increased hospital length of stay (incidence rate ratio = 1.15, 95% CI = 1.09-1.22, p < 0.001).

INTERPRETATION

Postoperative increases in blood-brain barrier permeability are independently associated with increased delirium rates and postoperative hospital length of stay. Although these findings do not establish causality, studies are warranted to determine whether interventions to reduce postoperative blood-brain barrier dysfunction would reduce postoperative delirium rates and hospital length of stay. ANN NEUROL 2023;94:1024-1035.

A Role for Blood-brain Barrier Dysfunction in Delirium following Non-Cardiac Surgery in Older adults

Objective

Although animal models suggest a role for blood-brain barrier dysfunction in postoperative delirium-like behavior, its role in postoperative delirium and postoperative recovery in humans is unclear. Thus, we evaluated the role of blood-brain barrier dysfunction in postoperative delirium and hospital length of stay among older surgery patients.

Methods

Cognitive testing, delirium assessment, and cerebrospinal fluid and blood sampling were prospectively performed before and after non-cardiac, non-neurologic surgery. Blood-brain barrier dysfunction was assessed using the cerebrospinal fluid-to-plasma albumin ratio (CPAR).

Results

Of 207 patients (median age 68, 45% female) with complete CPAR and delirium data, 26 (12.6%) developed postoperative delirium. Overall, CPAR increased from before to 24-hours after surgery (median postoperative change 0.28, [IQR] [-0.48-1.24]; Wilcoxon p=0.001). Preoperative to 24-hour postoperative change in CPAR was greater among patients who developed delirium vs those who did not (median [IQR] 1.31 [0.004, 2.34] vs 0.19 [-0.55, 1.08]; p=0.003). In a multivariable model adjusting for age, baseline cognition, and surgery type, preoperative to 24-hour postoperative change in CPAR was independently associated with delirium incidence (per CPAR increase of 1, OR = 1.30, [95% CI 1.03-1.63]; p=0.026) and increased hospital length of stay (IRR = 1.15 [95% CI 1.09-1.22]; p<0.001).

Interpretation

Postoperative increases in blood-brain barrier permeability are independently associated with increased delirium rates and postoperative hospital length of stay. Although these findings do not establish causality, studies are warranted to determine whether interventions to reduce postoperative blood-brain barrier dysfunction would reduce postoperative delirium rates and hospital length of stay.

CX3CL1 Pathway as a Molecular Target for Treatment Strategies in Alzheimer's Disease

Alzheimer's disease (AD) is a scourge for patients, caregivers and healthcare professionals due to the progressive character of the disease and the lack of effective treatments. AD is considered a proteinopathy, which means that aetiological and clinical features of AD have been linked to the deposition of amyloid β (Aβ) and hyperphosphorylated tau protein aggregates throughout the brain, with Aβ and hyperphosphorylated tau representing classical AD hallmarks. However, some other putative mechanisms underlying the pathogenesis of the disease have been proposed, including inflammation in the brain, microglia activation, impaired hippocampus neurogenesis and alterations in the production and release of neurotrophic factors. Among all, microglia activation and chronic inflammation in the brain gained some attention, with researchers worldwide wondering whether it is possible to prevent and stop, respectively, the onset and progression of the disease by modulating microglia phenotypes. The following key points have been established so far: (i) Aβ deposition in brain parenchyma represents repeated stimulus determining chronic activation of microglia; (ii) chronic activation and priming of microglia make these cells lose neuroprotective functions and favour damage and loss of neurons; (iii) quiescent status of microglia at baseline prevents chronic activation and priming, meaning that the more microglia are quiescent, the less they become neurotoxic. Many molecules are known to modulate the quiescent baseline state of microglia, attracting huge interest among scientists as to whether these molecules could be used as valuable targets in AD treatment. The downside of the coin came early with the observation that quiescent microglia do not display phagocytic ability, being unable to clear Aβ deposits since phagocytosis is crucial for Aβ clearance efficacy. A possible solution for this issue could be found in the modulation of microglia status at baseline, which could help maintain both neuroprotective features and phagocytic ability at the same time. Among the molecules known to influence the baseline status of microglia, C-X3-chemokine Ligand 1 (CX3CL1), also known as Fractalkine (FKN), is one of the most investigated. FKN and its microglial receptor CX3CR1 are crucial players in the interplay between neurons and microglia, modulating the operation of some neural circuits and the efficacy and persistence of immune response against injury. In addition, CX3CL1 regulates synaptic pruning and plasticity in the developmental age and in adulthood, when it strongly impacts the hippocampus neurogenesis of the adult. CX3CL1 has an effect on Aβ clearance and tau phosphorylation, as well as in microglia activation and priming. For all the above, CX3CL1/CX3CR1 signalling has been widely studied in relation to AD pathogenesis, and its biochemical pathway could hide molecular targets for novel treatment strategies in AD. This review summarizes the possible role of CX3CL1 in AD pathogenesis and its use as a potential target for AD treatment.

The Cytokine CX3CL1 and ADAMs/MMPs in Concerted Cross-Talk Influencing Neurodegenerative Diseases

Neuroinflammation plays a fundamental role in the development and progression of neurodegenerative diseases. It could therefore be said that neuroinflammation in neurodegenerative pathologies is not a consequence but a cause of them and could represent a therapeutic target of neuronal degeneration. CX3CL1 and several proteases (ADAMs/MMPs) are strongly involved in the inflammatory pathways of these neurodegenerative pathologies with multiple effects. On the one hand, ADAMs have neuroprotective and anti-apoptotic effects; on the other hand, they target cytokines and chemokines, thus causing inflammatory processes and, consequently, neurodegeneration. CX3CL1 itself is a cytokine substrate for the ADAM, ADAM17, which cleaves and releases it in a soluble isoform (sCX3CL1). CX3CL1, as an adhesion molecule, on the one hand, plays an inhibiting role in the pro-inflammatory response in the central nervous system (CNS) and shows neuroprotective effects by binding its membrane receptor (CX3CR1) present into microglia cells and maintaining them in a quiescent state; on the other hand, the sCX3CL1 isoform seems to promote neurodegeneration. In this review, the dual roles of CX3CL1 and ADAMs/MMPs in different neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (MH), and multiple sclerosis (MS), are investigated.

TREM2 and Microglia Contribute to the Synaptic Plasticity: from Physiology to Pathology

Synapses are bridges for information transmission in the central nervous system (CNS), and synaptic plasticity is fundamental for the normal function of synapses, contributing substantially to learning and memory. Numerous studies have proven that microglia can participate in the occurrence and progression of neurodegenerative diseases (NDDs), such as Alzheimer's disease (AD), by regulating synaptic plasticity. In this review, we summarize the main characteristics of synapses and synaptic plasticity under physiological and pathological conditions. We elaborate the origin and development of microglia and the two well-known microglial signaling pathways that regulate synaptic plasticity. We also highlight the unique role of triggering receptor expressed on myeloid cells 2 (TREM2) in microglia-mediated regulation of synaptic plasticity and its relationship with AD. Finally, we propose four possible ways in which TREM2 is involved in regulating synaptic plasticity. This review will help researchers understand how NDDs develop from the perspective of synaptic plasticity.

Microglia-Mediated Neurovascular Unit Dysfunction in Alzheimer's Disease

The neurovascular unit (NVU) is involved in the pathological changes in Alzheimer's disease (AD). The NVU is a structural and functional complex that maintains microenvironmental homeostasis and metabolic balance in the central nervous system. As one of the most important components of the NVU, microglia not only induce blood-brain barrier breakdown by promoting neuroinflammation, the infiltration of peripheral white blood cells and oxidative stress but also mediate neurovascular uncoupling by inducing mitochondrial dysfunction in neurons, abnormal contraction of cerebral vessels, and pericyte loss in AD. In addition, microglia-mediated dysfunction of cellular components in the NVU, such as astrocytes and pericytes, can destroy the integrity of the NVU and lead to NVU impairment. Therefore, we review the mechanisms of microglia-mediated NVU dysfunction in AD. Furthermore, existing therapeutic advancements aimed at restoring the function of microglia and the NVU in AD are discussed. Finally, we predict the role of pericytes in microglia-mediated NVU dysfunction in AD is the hotspot in the future.

The Complement System in the Central Nervous System: From Neurodevelopment to Neurodegeneration

The functions of the complement system to both innate and adaptive immunity through opsonization, cell lysis, and inflammatory activities are well known. In contrast, the role of complement in the central nervous system (CNS) which extends beyond immunity, is only beginning to be recognized as important to neurodevelopment and neurodegeneration. In addition to protecting the brain against invasive pathogens, appropriate activation of the complement system is pivotal to the maintenance of normal brain function. Moreover, overactivation or dysregulation may cause synaptic dysfunction and promote excessive pro-inflammatory responses. Recent studies have provided insights into the various responses of complement components in different neurological diseases and the regulatory mechanisms involved in their pathophysiology, as well as a glimpse into targeting complement factors as a potential therapeutic modality. However, there remain significant knowledge gaps in the relationship between the complement system and different brain disorders. This review summarizes recent key findings regarding the role of different components of the complement system in health and pathology of the CNS and discusses the therapeutic potential of anti-complement strategies for the treatment of neurodegenerative conditions.

Crosstalk between Microglia and Neurons in Neurotrauma: An Overview of the Underlying Mechanisms

Microglia are the resident immune cells of the brain and play a crucial role in housekeeping and maintaining homeostasis of the brain microenvironment. Upon injury or disease, microglial cells become activated, at least partly, via signals initiated by injured neurons. Activated microglia, thereby, contribute to both neuroprotection and neuroinflammation. However, sustained microglial activation initiates a chronic neuroinflammatory response which can disturb neuronal health and disrupt communications between neurons and microglia. Thus, microglia-neuron crosstalk is critical in a healthy brain as well as during states of injury or disease. As most studies focus on how neurons and microglia act in isolation during neurotrauma, there is a need to understand the interplay between these cells in brain pathophysiology. This review highlights how neurons and microglia reciprocally communicate under physiological conditions and during brain injury and disease. Furthermore, the modes of microglia-neuron communication are exposed, focusing on cell-contact dependent signaling and communication by the secretion of soluble factors like cytokines and growth factors. In addition, it has been discussed that how microglia-neuron interactions could exert either beneficial neurotrophic effects or pathologic proinflammatory responses. We further explore how aberrations in microglia-neuron crosstalk may be involved in central nervous system (CNS) anomalies, namely traumatic brain injury (TBI), neurodegeneration, and ischemic stroke. A clear understanding of how the microglia-neuron crosstalk contributes to the pathogenesis of brain pathologies may offer novel therapeutic avenues of brain trauma treatment.

Dysregulated protein phosphorylation: A determining condition in the continuum of brain aging and Alzheimer's disease

Tau hyperphosphorylation is the first step of neurofibrillary tangle (NFT) formation. In the present study, samples of the entorhinal cortex (EC) and frontal cortex area 8 (FC) of cases with NFT pathology classified as stages I-II, III-IV, and V-VI without comorbidities, and of middle-aged (MA) individuals with no NFT pathology, were analyzed by conventional label-free and SWATH-MS (sequential window acquisition of all theoretical fragment ion spectra mass spectrometry) to assess the (phospho)proteomes. The total number of identified dysregulated phosphoproteins was 214 in the EC, 65 of which were dysregulated at the first stages (I-II) of NFT pathology; 167 phosphoproteins were dysregulated in the FC, 81 of them at stages I-II of NFT pathology. A large percentage of dysregulated phosphoproteins were identified in the two regions and at different stages of NFT progression. The main group of dysregulated phosphoproteins was made up of components of the membranes, cytoskeleton, synapses, proteins linked to membrane transport and ion channels, and kinases. The present results show abnormal phosphorylation of proteins at the first stages of NFT pathology in the elderly (in individuals clinically considered representative of normal aging) and sporadic Alzheimer's disease (sAD). Dysregulated protein phosphorylation in the FC precedes the formation of NFTs and SPs. The most active period of dysregulated phosphorylation is at stages III-IV when a subpopulation of individuals might be clinically categorized as suffering from mild cognitive impairment which is a preceding determinant stage in the progression to dementia. Altered phosphorylation of selected proteins, carried out by activation of several kinases, may alter membrane and cytoskeletal functions, among them synaptic transmission and membrane/cytoskeleton signaling. Besides their implications in sAD, the present observations suggest a molecular substrate for "benign" cognitive deterioration in "normal" brain aging.

Inflammation and Parkinson's disease pathogenesis: Mechanisms and therapeutic insight

After Alzheimer's disease, Parkinson's disease is the most frequent neurodegenerative disorder. Although numerous treatments have been developed to control the disease symptomatology, with some successes, an efficacious therapy affecting the causes of PD is still a goal to pursue. The genetic evidence and the identification of α-synuclein as the main component of intracellular Lewy bodies, the neuropathological hallmark of PD and related disorders, have changed the approach to these disorders. More recently, the detrimental role of α-synuclein has been further extended to explain the wide spread of cerebral pathology through its oligomers. To emphasize the central pathogenic role of these soluble aggregates, we have defined synucleinopathies and other neurodegenerative disorders associated with protein misfolding as oligomeropathies. Another common element in the pathogenesis of oligomeropathies is the role played by inflammation, both at the peripheral and cerebral levels. In the brain parenchyma, inflammatory reaction has been considered an obvious consequence of neuronal degeneration, but recent observations indicate a direct contribution of glial alteration in the early phase of the disease. Furthermore, systemic inflammation also influences the development of neuronal dysfunction caused by specific elements, β amyloid, α-synuclein, tau or prion. However, each disorder has its own specific pathological process and within the same pathological condition, it is possible to find inter-individual differences. This heterogeneity might explain the difficulties developing efficacious therapeutic approaches, even though the possibility of intervention is supported by robust biological evidence. We have recently demonstrated that peripheral inflammation can amplify the neuronal dysfunction induced by α-synuclein oligomers and the neuropathological consequences observed in a Parkinson's disease model. In both cases, activation of microglia was incremented by the "double hit" process, compared to the single treatment. In contrast, astrocyte activation was attenuated and these cells appeared damaged when chronic inflammation was combined with α-synuclein exposure. This evidence might indicate a more specific anti-inflammatory strategy rather than the generic anti-inflammatory treatment.

Maresin 1 attenuates pro-inflammatory activation induced by β-amyloid and stimulates its uptake

Alzheimer's disease (AD) is the most common dementia, characterized by pathological accumulation of β‐amyloid (Aβ) and hyperphosphorylation of tau protein, together with a damaging chronic inflammation. The lack of effective treatments urgently warrants new therapeutic strategies. Resolution of inflammation, associated with beneficial and regenerative activities, is mediated by specialized pro‐resolving lipid mediators (SPMs) including maresin 1 (MaR1). Decreased levels of MaR1 have been observed in AD brains. However, the pro‐resolving role of MaR1 in AD has not been fully investigated. In the present study, human monocyte‐derived microglia (MdM) and a differentiated human monocyte cell line (THP‐1 cells) exposed to Aβ were used as models of AD neuroinflammation. We have studied the potential of MaR1 to inhibit pro‐inflammatory activation of Aβ and assessed its ability to stimulate phagocytosis of Aβ₄₂. MaR1 inhibited the Aβ₄₂‐induced increase in cytokine secretion and stimulated the uptake of Aβ₄₂ in both MdM and differentiated THP‐1 cells. MaR1 was also found to decrease chemokine secretion and reduce the associated increase in the activation marker CD40. Activation of kinases involved in transduction of inflammation was not affected by MaR1, but the activity of nuclear factor (NF)‐κB was decreased. Our data show that MaR1 exerts effects that indicate a pro‐resolving role in the context of AD and thus presents itself as a potential therapeutic target for AD.

Microglial autophagy is impaired by prolonged exposure to β-amyloid peptides: evidence from experimental models and Alzheimer's disease patients

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by the presence of misfolded proteins, amyloid-β (Aβ) aggregates, and neuroinflammation in the brain. Microglial cells are key players in the context of AD, being capable of releasing cytokines in response to Aβ and degrading aggregated proteins by mechanisms involving the ubiquitin-proteasome system and autophagy. Here, we present in vivo and in vitro evidence showing that microglial autophagy is affected during AD progression. PDAPPJ20 mice-murine model of AD-exhibited an accumulation of the autophagy receptor p62 and ubiquitin+ aggregates in Iba1+ microglial cells close to amyloid deposits in the hippocampus. Moreover, cultured microglial BV-2 cells showed an enhanced autophagic flux during a 2-h exposure to fibrillar Aβ, which was decreased if the exposure was prolonged to 24 h, a condition analogous to the chronic exposure to Aβ in the human pathology. The autophagic impairment was also associated with lysosomal damage, depicted by membrane permeabilization as shown by the presence of the acid hydrolase cathepsin-D in cytoplasm and altered LysoTracker staining. These results are compatible with microglial exhaustion caused by pro-inflammatory conditions and persistent exposure to aggregated Aβ peptides. In addition, we found LC3-positive autophagic vesicles accumulated in phagocytic CD68+ microglia in human AD brain samples, suggesting defective autophagy in microglia of AD brain. Our results indicate that the capacity of microglia to degrade Aβ and potentially other proteins through autophagy may be negatively affected as the disease progresses. Preserving autophagy in microglia thus emerges as a promising approach for treating AD. Graphical abstract.

Trans-cinnamaldehyde improves neuroinflammation-mediated NMDA receptor dysfunction and memory deficits through blocking NF-κB pathway in presenilin1/2 conditional double knockout mice

A chronic neuroinflammatory response has been considered as a critical pathogenesis promoting neurodegenerative progression in Alzheimer's disease (AD). During neuroinflammatory process, microglia are excessively activated and simultaneously release numerous pro-inflammatory mediators that cause synaptic dysfunction in the forebrain prior to neuronal degeneration and memory deficits in AD. Thus, prevention of neuroinflammation-mediated synaptic dysfunction may be a potential therapeutic approach against neurodegenerative disorders. Trans-cinnamaldehyde (TCA) is a primary bioactive component derived from the stem bark of Cinnamomum cassia, and it possesses potent anti-inflammatory and neuroprotective activities in in vivo and in vitro experiments. However, the in-depth molecular mechanisms of TCA underlying anti-neuroinflammatory and neuroprotective effects on memory deficits in AD are still unclear. The presenilin 1 and 2 conditional double knockout (PS cDKO) mice exhibit AD-like phenotypes including obvious neuroinflammatory responses and synaptic dysfunction and memory deficits. Here, PS cDKO were used to evaluate the potential neuroprotective effects of TCA against neuroinflammation-mediated dementia by performing behavioral tests, electrophysiological recordings and molecular biology analyses. We observed that TCA treatment reversed abnormal expression of synaptic proteins and tau hyperphosphorylation in the hippocampus and prefrontal cortex of PS cDKO mice. TCA treatment also ameliorated NMDA receptor (NMDAR) dysfunction including impaired NMDAR-mediated responses and long-term potentiation (LTP) induction in the hippocampus of PS cDKO mice. Moreover, TCA possesses an ability to suppress neuroinflammatory responses by diminishing microglial activation and levels of pro-inflammatory mediators in the hippocampus and prefrontal cortex of PS cDKO mice. Importantly, improving NMDAR dysfunction and memory deficits of PS cDKO mice was due to the inhibition of neuroinflammatory responses through TCA's interruptive effect on the nuclear factor kappa B (NF-κB) signaling pathway. Therefore, TCA may be a potential anti-neuroinflammatory agent for deterring neurodegenerative progression of AD.

Bidirectional Microglia-Neuron Communication in Health and Disease

Microglia are ramified cells that exhibit highly motile processes, which continuously survey the brain parenchyma and react to any insult to the CNS homeostasis. Although microglia have long been recognized as a crucial player in generating and maintaining inflammatory responses in the CNS, now it has become clear, that their function are much more diverse, particularly in the healthy brain. The innate immune response and phagocytosis represent only a little segment of microglia functional repertoire that also includes maintenance of biochemical homeostasis, neuronal circuit maturation during development and experience-dependent remodeling of neuronal circuits in the adult brain. Being equipped by numerous receptors and cell surface molecules microglia can perform bidirectional interactions with other cell types in the CNS. There is accumulating evidence showing that neurons inform microglia about their status and thus are capable of controlling microglial activation and motility while microglia also modulate neuronal activities. This review addresses the topic: how microglia communicate with other cell types in the brain, including fractalkine signaling, secreted soluble factors and extracellular vesicles. We summarize the current state of knowledge of physiological role and function of microglia during brain development and in the mature brain and further highlight microglial contribution to brain pathologies such as Alzheimer’s and Parkinson’s disease, brain ischemia, traumatic brain injury, brain tumor as well as neuropsychiatric diseases (depression, bipolar disorder, and schizophrenia).

An updated Alzheimer hypothesis: Complement C3 and risk of Alzheimer's disease-A cohort study of 95,442 individuals

INTRODUCTION

We tested the hypothesis that low plasma complement C3 is observationally and genetically associated with high risk of Alzheimer's disease (AD).

METHODS

We studied 95,442 individuals enrolled in the Copenhagen General Population Study. In genetic analyses, we further included 8367 individuals from the Copenhagen City Heart Study. In the two studies, 1189 and 35 developed AD during median 8 years follow-up.

RESULTS

The multifactorially adjusted hazard ratio for risk of AD for a one standard deviation lower levels of complement C3 was 1.11 (95% confidence interval: 1.04-1.19) in all individuals and 1.66 (1.33-2.07) in APOE ε44 carriers. In Mendelian randomization, the corresponding genetic estimates were 1.66 (1.05-2.63) overall and 1.99 (0.52-7.65) in APOE ε44 carriers.

DISCUSSION

Low baseline levels of complement C3 were associated with high risk of AD. The risk was amplified in APOE ε44 highly susceptible individuals, and these findings were substantiated by a Mendelian randomization approach, potentially implying causality. Based on these findings, we present and thoroughly discuss an updated Alzheimer hypothesis incorporating low complement C3 levels.

Alzheimer's Disease, Oligomers, and Inflammation

The production of soluble amyloid-β oligomers (AβOs) and the activation of inflammation are two important early steps in the pathogenesis of Alzheimer's disease (AD). The central role of oligomers as responsible for the neuronal dysfunction associated with the clinical features has been extended to the other protein misfolding disorders definable, on this basis, as oligomeropathies. In AD, recent evidence indicates that the mechanism of inflammation as a consequence of neurodegeneration must be assessed in favor of a more direct role of glial activation in the alteration of synaptic function. Our own experimental models demonstrate the efficacy of anti-inflammatory treatments in preventing the cognitive deficits induced acutely by AβOs applied directly in the brain. Moreover, some promising clinical tools are based on immunological activation reducing the presence of cerebral Aβ deposits. However, the strategies based on the control of inflammatory factors as well as the amyloid aggregation show poor or non-therapeutic efficacy. Numerous studies have examined inflammatory factors in biological fluids as possible markers of the neuroinflammation in AD. In some cases, altered levels of cytokines or other inflammatory markers in cerebrospinal fluid correlate with the severity of the disease. Here we propose, according to the precision medicine principles, innovative therapeutic approaches to AD based on the patient's inflammatory profile/state. The earlier intervention and a multifactor approach are two other elements considered essential to improve the chances of effective therapy in AD.

A Critical Assessment of Research on Neurotransmitters in Alzheimer's Disease

The purpose of this mini-forum, "Neurotransmitters and Alzheimer's Disease", is to critically assess the current status of neurotransmitters in Alzheimer's disease. Neurotransmitters are essential neurochemicals that maintain synaptic and cognitive functions in mammals, including humans, by sending signals across pre- to post-synaptic neurons. Authorities in the fields of synapses and neurotransmitters of Alzheimer's disease summarize the current status of basic biology of synapses and neurotransmitters, and also update the current status of clinical trials of neurotransmitters in Alzheimer's disease. This article discusses the prevalence, economic impact, and stages of Alzheimer's dementia in humans.