Pro-inflammatory conditions promote neuronal damage mediated by Amyloid Precursor Protein and decrease its phagocytosis and degradation by microglial cells in culture

Vagus nerve stimulation (VNS) preventing postoperative cognitive dysfunction (POCD): two potential mechanisms in cognitive function

Postoperative cognitive dysfunction (POCD) impacts a significant number of patients annually, frequently impairing their cognitive abilities and resulting in unfavorable clinical outcomes. Aimed at addressing cognitive impairment, vagus nerve stimulation (VNS) is a therapeutic approach, which was used in many mental disordered diseases, through the modulation of vagus nerve activity. In POCD model, the enhancement of cognition function provided by VNS was shown, demonstrating VNS effect on cognition in POCD. In the present study, we primarily concentrates on elucidating the role of the VNS improving the cognitive function in POCD, via two potential mechanisms: the inflammatory microenvironment and epigenetics. This study provided a theoretical support for the feasibility that VNS can be a potential method to enhance cognition function in POCD.

Microglial reactivity in brainstem chemosensory nuclei in response to hypercapnia

Microglia, the resident immune cells of the CNS, surveil, detect, and respond to various extracellular signals. Depending on the nature of these signals, an integrative microglial response can be triggered, resulting in a phenotypic transformation. Here, we evaluate whether hypercapnia modifies microglia phenotype in brainstem respiratory-related nuclei. Adult C57BL/6 inbred mice were exposed to 10% CO2 enriched air (hypercapnia), or pure air (control), for 10 or 30 min and immediately processed for immunohistochemistry to detect the ubiquitous microglia marker, ionized calcium binding adaptor molecule 1 (Iba1). Hypercapnia for thirty, but not 10 min reduced the Iba1 labeling percent coverage in the ventral respiratory column (VRC), raphe nucleus (RN), and nucleus tractus solitarius (NTS) and the number of primary branches in VRC. The morphological changes persisted, at least, for 60 min breathing air after the hypercapnic challenge. No significant changes were observed in Iba1+ cells in the spinal trigeminal nucleus (Sp5) and the hippocampus. In CF-1 outbred mice, 10% CO2 followed by 60 min of breathing air, resulted in the reduction of Iba1 labeling percent coverage and the number and length of primary branches in VRC, RN, and NTS. No morphological change was observed in Iba1+ cells in Sp5 and hippocampus. Double immunofluorescence revealed that prolonged hypercapnia increased the expression of CD86, an inflammatory marker for reactive state microglia, in Iba1+ cells in VRC, RN, and NTS, but not in Sp5 and hippocampus in CF-1 mice. By contrast, the expression of CD206, a marker of regulatory state microglia, persisted unmodified. In brainstem, but not in hippocampal microglia cultures, hypercapnia increased the level of IL1β, but not that of TGFβ measured by ELISA. Our results show that microglia from respiratory-related chemosensory nuclei, are reactive to prolonged hypercapnia acquiring an inflammatory-like phenotype.

Aging Microglia and Their Impact in the Nervous System

Aging is the greatest risk factor for neurodegenerative diseases. Microglia are the resident immune cells in the central nervous system (CNS), playing key roles in its normal functioning, and as mediators for age-dependent changes of the CNS, condition at which they generate a hostile environment for neurons. Transforming Growth Factor β1 (TGFβ1) is a regulatory cytokine involved in immuneregulation and neuroprotection, affecting glial cell inflammatory activation, neuronal survival, and function. TGFβ1 signaling undergoes age-dependent changes affecting the regulation of microglial cells and can contribute to the pathophysiology of neurodegenerative diseases. This chapter focuses on assessing the role of age-related changes on the regulation of microglial cells and their impact on neuroinflammation and neuronal function, for understanding age-dependent changes of the nervous system.

Neuroinflammation: The central enabler of postoperative cognitive dysfunction

The proportion of advanced age patients undergoing surgical procedures is on the rise owing to advancements in surgical and anesthesia technologies as well as an overall aging population. As a complication of anesthesia and surgery, older patients frequently suffer from postoperative cognitive dysfunction (POCD), which may persist for weeks, months or even longer. POCD is a complex pathological process involving multiple pathogenic factors, and its mechanism is yet unclear. Potential theories include inflammation, deposition of pathogenic proteins, imbalance of neurotransmitters, and chronic stress. The identification, prevention, and treatment of POCD are still in the exploratory stages owing to the absence of standardized diagnostic criteria. Undoubtedly, comprehending the development of POCD remains crucial in overcoming the illness. Neuroinflammation is the leading hypothesis and a crucial component of the pathological network of POCD and may have complex interactions with other mechanisms. In this review, we discuss the possible ways in which surgery and anesthesia cause neuroinflammation and investigate the connection between neuroinflammation and the development of POCD. Understanding these mechanisms may likely ensure that future treatment options of POCD are more effective.

The CRISPR-Cas9 crATIC HeLa transcriptome: Characterization of a novel cellular model of ATIC deficiency and ZMP accumulation

In de novo purine biosynthesis (DNPS), 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase (EC 2.1.2.3)/inosine monophosphate cyclohydrolase (EC 3.5.4.10) (ATIC) catalyzes the last two reactions of the pathway: conversion of 5-aminoimidazole-4-carboxamide ribonucleotide [aka Z-nucleotide monophosphate (ZMP)] to 5-formamido-4-imidazolecarboxamide ribonucleotide (FAICAR) then to inosine monophosphate (IMP). Mutations in ATIC cause an untreatable and devastating inborn error of metabolism in humans. ZMP is an adenosine monophosphate (AMP) mimetic and a known activator of AMP-activated protein kinase (AMPK). Recently, a HeLa cell line null mutant for ATIC was constructed via CRISPR-Cas9 mutagenesis. This mutant, crATIC, accumulates ZMP during purine starvation. Given that the mutant can accumulate ZMP in the absence of treatment with exogenous compounds, crATIC is likely an important cellular model of DNPS inactivation and ZMP accumulation. In the current study, we characterize the crATIC transcriptome versus the HeLa transcriptome in purine-supplemented and purine-depleted growth conditions. We report and discuss transcriptome changes with particular relevance to Alzheimer's disease and in genes relevant to lipid and fatty acid synthesis, neurodevelopment, embryogenesis, cell cycle maintenance and progression, extracellular matrix, immune function, TGFβ and other cellular processes.

[Quercetin ameliorates inflammation in CA1 hippocampal region in aged triple transgenic Alzheimer´s disease mice model.]

INTRODUCTION

Alzheimer's disease is the most common form of dementia. It is characterized by histopathological hallmarks such as senile plaques and neurofibrillary tangles, as well as a concomitant activation of microglial cells and astrocytes that release pro-inflammatory mediators such as IL-1β, iNOS, and COX-2, leading to neuronal dysfunction and death.

OBJECTIVE

To evaluate the effect of quercetin on the inflammatory response in the CA1 area of the hippocampus in a 3xTg-AD male and female mice model.

MATERIALS AND METHODS

Animals were injected intraperitoneally with quercetin every 48 hours during three months, and we conducted histological and biochemical studies.

RESULTS

We found that in quercetin-treated 3xTg-AD mice, reactive microglia and fluorescence intensity of Aβ aggregates significantly decreased. GFAP, iNOS, and COX-2 immunoreactivity also decreased and we observed a clear tendency in the reduction of IL-1β in hippocampal lysates.

CONCLUSION

Our work suggests an anti-inflammatory effect of quercetin in the CA1 hippocampal region of aged triple transgenic Alzheimer's disease mice.

Involvement of the Bradykinin B1 Receptor in Microglial Activation: In Vitro and In Vivo Studies

The importance of brain inflammation to Alzheimer's disease (AD) pathogenesis has been accepted of late, with it currently being held that brain inflammation aggravates AD pathology. One important aspect of brain inflammation is the recruitment and activation of microglia, a process termed microgliosis. Kinins and bradykinin (BK), in particular, are major pro-inflammatory mediators in the periphery, although all of the factors comprising the kinin system have also been described in the brain. Moreover, it was shown that the amyloid β (Aβ) peptide (a component of AD plaques) enhances kinin secretion and activates BK receptors that can, in turn, stimulate Aβ production. Still, the role of bradykinin in modulating brain inflammation and AD is not completely understood. In this study, we aimed to investigate the roles of the bradykinin B₁ receptor (B₁R) and bradykinin B₂ receptor (B₂R) in regulating microglial secretion of pro-inflammatory factors in vitro. Furthermore, the effects of intranasal administration of specific B₁R and B₂R antagonists on Aβ burden and microglial accumulation in the brains of transgenic AD mice were studied. The data obtained show that neither R-715 (a B₁R antagonist) nor HOE 140 (a B₂R antagonist) altered microglial cell viability. However, R-715, but not HOE 140, markedly increased lipopolysaccharide-induced nitric oxide (NO) and tumor necrosis factor-alpha (TNF-α) release, as well as inducible nitric oxide synthase expression in BV2 microglial cells. Neither antagonist altered NO nor TNF-α production in non-stimulated cells. We also showed that intranasal administration of R-715 but not HOE 140 to 8-week-old 5X familial AD mice enhanced amyloid burden and microglia/macrophage accumulation in the cortex. To conclude, we provide evidence supporting a role of B₁R in brain inflammation and in the regulation of amyloid deposition in AD mice, possibly with microglial/macrophage involvement. Further studies are required to test whether modulation of this receptor can serve as a novel therapeutic strategy for AD.

Role of TGFβ signaling in the pathogenesis of Alzheimer's disease

Aging is the main risk factor for Alzheimer’s disease (AD); being associated with conspicuous changes on microglia activation. Aged microglia exhibit an increased expression of cytokines, exacerbated reactivity to various stimuli, oxidative stress, and reduced phagocytosis of β-amyloid (Aβ). Whereas normal inflammation is protective, it becomes dysregulated in the presence of a persistent stimulus, or in the context of an inflammatory environment, as observed in aging. Thus, neuroinflammation can be a self-perpetuating deleterious response, becoming a source of additional injury to host cells in neurodegenerative diseases. In aged individuals, although transforming growth factor β (TGFβ) is upregulated, its canonical Smad3 signaling is greatly reduced and neuroinflammation persists. This age-related Smad3 impairment reduces protective activation while facilitating cytotoxic activation of microglia through several cellular mechanisms, potentiating microglia-mediated neurodegeneration. Here, we critically discuss the role of TGFβ-Smad signaling on the cytotoxic activation of microglia and its relevance in the pathogenesis of AD. Other protective functions, such as phagocytosis, although observed in aged animals, are not further induced by inflammatory stimuli and TGFβ1. Analysis in silico revealed that increased expression of receptor scavenger receptor (SR)-A, involved in Aβ uptake and cell activation, by microglia exposed to TGFβ, through a Smad3-dependent mechanism could be mediated by transcriptional co-factors Smad2/3 over the MSR1 gene. We discuss that changes of TGFβ-mediated regulation could at least partially mediate age-associated microglia changes, and, together with other changes on inflammatory response, could result in the reduction of protective activation and the potentiation of cytotoxicity of microglia, resulting in the promotion of neurodegenerative diseases.

Microglia in Glia-Neuron Co-cultures Exhibit Robust Phagocytic Activity Without Concomitant Inflammation or Cytotoxicity

A simple method to co-culture granule neurons and glia from a single brain region is described, and microglia activation profiles are assessed in response to naturally occurring neuronal apoptosis, excitotoxin-induced neuronal death, and lipopolysaccharide (LPS) addition. Using neonatal rat cerebellar cortex as a tissue source, glial proliferation is regulated by omission or addition of the mitotic inhibitor cytosine arabinoside (AraC). After 7-8 days in vitro, microglia in AraC(-) cultures are abundant and activated based on their amoeboid morphology, expressions of ED1 and Iba1, and ability to phagocytose polystyrene beads and the majority of neurons undergoing spontaneous apoptosis. Microglia and phagocytic activities are sparse in AraC(+) cultures. Following exposure to excitotoxic kainate concentrations, microglia in AraC(-) cultures phagocytose most dead neurons within 24 h without exacerbating neuronal loss or mounting a strong or sustained inflammatory response. LPS addition induces a robust inflammatory response, based on microglial expressions of TNF-α, COX-2 and iNOS proteins, and mRNAs, whereas these markers are essentially undetectable in control cultures. Thus, the functional effector state of microglia is primed for phagocytosis but not inflammation or cytotoxicity even after kainate exposure that triggers death in the majority of neurons. This model should prove useful in studying the progressive activation states of microglia and factors that promote their conversion to inflammatory and cytotoxic phenotypes.

Chronic exposure to TGFβ1 regulates myeloid cell inflammatory response in an IRF7-dependent manner

Tissue microenvironment influences the function of resident and infiltrating myeloid-derived cells. In the central nervous system (CNS), resident microglia and freshly recruited infiltrating monocyte-derived macrophages (mo-MΦ) display distinct activities under pathological conditions, yet little is known about the microenvironment-derived molecular mechanism that regulates these differences. Here, we demonstrate that long exposure to transforming growth factor-β1 (TGFβ1) impaired the ability of myeloid cells to acquire a resolving anti-inflammatory phenotype. Using genome-wide expression analysis and chromatin immunoprecipitation followed by next-generation sequencing, we show that the capacity to undergo pro- to anti-inflammatory (M1-to-M2) phenotype switch is controlled by the transcription factor interferon regulatory factor 7 (IRF7) that is down-regulated by the TGFβ1 pathway. RNAi-mediated perturbation of Irf7 inhibited the M1-to-M2 switch, while IFNβ1 (an IRF7 pathway activator) restored it. In vivo induction of Irf7 expression in microglia, following spinal cord injury, reduced their pro-inflammatory activity. These results highlight the key role of tissue-specific environmental factors in determining the fate of resident myeloid-derived cells under both physiological and pathological conditions.

Role of scavenger receptors in glia-mediated neuroinflammatory response associated with Alzheimer's disease

It is widely accepted that cells serving immune functions in the brain, namely, microglia and astrocytes, are important mediators of pathological phenomena observed in Alzheimer's disease. However, it is unknown how these cells initiate the response that results in cognitive impairment and neuronal degeneration. Here, we review the participation of the immune response mediated by glial cells in Alzheimer's disease and the role played by scavenger receptors in the development of this pathology, focusing on the relevance of class A scavenger receptor (SR-A) for A β clearance and inflammatory activation of glial cell, and as a potential target for Alzheimer's disease therapy.

Scavenger receptor class A ligands induce secretion of IL1β and exert a modulatory effect on the inflammatory activation of astrocytes in culture

Class-A scavenger receptor (SR-A) is expressed by microglia, and we show here that it is also expressed by astrocytes, where it participates on their inflammatory activation. Astrocytes play a key role on the inflammatory response of the central nervous system, secreting several soluble mediators like cytokines and radical species. Exposure to SR ligands activated MAPKs and NF-κB signaling and increased production of IL1β and nitric oxide (NO). IL1β classically an inflammatory cytokine surprisingly did not increase but inhibited LPS+IFNγ-induced NO production by astrocytes. Our results suggest that SRs expressed by astrocytes participate in the modulation of inflammatory activation.

Modulation of interferon-γ-induced glial cell activation by transforming growth factor β1: a role for STAT1 and MAPK pathways

Overactivated glial cells can produce neurotoxic oxidant molecules such as nitric oxide (NO·) and superoxide anion (O(2)·(-)). We have previously reported that transforming growth factor β1 (TGFβ1) released by hippocampal cells modulates interferon-γ (IFNγ)-induced production of O(2)·(-) and NO· by glial cells. However, underlying molecular mechanisms are not completely understood, thereby, the aim of this work was to study the effect of TGFβ1 on IFNγ-induced signaling pathways. We found that costimulation with TGFβ1 decreased IFNγ-induced phosphorylation of signal transducer and activator of transcription-type-1 (STAT1) and extracellular signal-regulated kinase (ERK), which correlated with a reduced O(2)·(-) and NO· production in mixed and purified glial cultures. Moreover, IFNγ caused a decrease in TGFβ1-mediated phosphorylation of P38, whereas pre-treatment with ERK and P38 inhibitors decreased IFNγ-induced phosphorylation of STAT1 on serine727 and production of radical species. These results suggested that modulation of glial activation by TGFβ1 is mediated by deactivation of MAPKs. Notably, TGFβ1 increased the levels of MAPK phosphatase-1 (MKP-1), whose participation in TGFβ1-mediated modulation was confirmed by MKP-1 siRNA transfection in mixed and purified glial cultures. Our results indicate that the cross-talk between IFNγ and TGFβ1 might regulate the activation of glial cells and that TGFβ1 modulated IFNγ-induced production of neurotoxic oxidant molecules through STAT1, ERK, and P38 pathways.

Alzheimer's disease: redox dysregulation as a common denominator for diverse pathogenic mechanisms

Alzheimer's disease (AD) is the most common cause of dementia and a progressive neurodegeneration that appears to result from multiple pathogenic mechanisms (including protein misfolding/aggregation, involved in both amyloid β-dependent senile plaques and tau-dependent neurofibrillary tangles), metabolic and mitochondrial dysfunction, excitoxicity, calcium handling impairment, glial cell dysfunction, neuroinflammation, and oxidative stress. Oxidative stress, which could be secondary to several of the other pathophysiological mechanisms, appears to be a major determinant of the pathogenesis and progression of AD. The identification of oxidized proteins common for mild cognitive impairment and AD suggests that key oxidation pathways are triggered early and are involved in the initial progression of the neurodegenerative process. Abundant data support that oxidative stress, also considered as a main factor for aging, the major risk factor for AD, can be a common key element capable of articulating the divergent nature of the proposed pathogenic factors. Pathogenic mechanisms influence each other at different levels. Evidence suggests that it will be difficult to define a single-target therapy resulting in the arrest of progression or the improvement of AD deterioration. Since oxidative stress is present from early stages of disease, it appears as one of the main targets to be included in a clinical trial. Exploring the articulation of AD pathogenic mechanisms by oxidative stress will provide clues for better understanding the pathogenesis and progression of this dementing disorder and for the development of effective therapies to treat this disease.

Aβ potentiates inflammatory activation of glial cells induced by scavenger receptor ligands and inflammatory mediators in culture

Alzheimer disease (AD) is a neurodegenerative disorder characterized by the accumulation of β amyloid (Aβ) aggregates. Aβ induces the inflammatory activation of glia, inducing secretion of Interleukin 1β (IL1β), nitric oxide (NO) and superoxide radicals. The specific receptor responsible for the induction of inflammatory activation by Aβ, is still an open question. We propose that scavenger receptors (SR) participate in the activation of glia by Aβ. We assessed production of NO, synthesis of IL1β and activation of ERK, JNK and NF-κB signaling pathways by Western blot, in primary rat glial cultures exposed to SR ligands (fucoidan and Poly I), LPS + IFNγ (LI), and Aβ. Poly I but not fucoidan nor fibrillar Aβ increased threefold NO production by astrocytes in a time-dependent manner. Fucoidan and Poly I increased 5.5- and 3.5-fold NO production by microglia, and co-stimulation with Aβ increased an additional 60% NO induced by SR ligands. Potentiation by Aβ was observed later for astrocytes than for microglia. In astrocytes, co-stimulation with Aβ potentiated ERK and JNK activation in response to Fucoidan and Poly I, whereas it reduced induction of JNK activation by LI and left unaffected NF-κB activation induced by LI. Levels of pro-IL1β in astrocytes increased with Aβ, SR ligands and LI, and were potentiated by co-stimulation with Aβ. Our results suggest that SRs play a role on inflammatory activation, inducing production of NO and IL1β, and show potentiation by Aβ. Potentiation of the inflammatory response of Aβ could be meaningful for the activation of glia observed in AD.

Neurobiology of vascular dementia

Vascular dementia is, in its current conceptual form, a distinct type of dementia with a spectrum of specific clinical and pathophysiological features. However, in a very large majority of cases, these alterations occur in an already aged brain, characterized by a milieu of cellular and molecular events common for different neurodegenerative diseases. The cell signaling defects and molecular dyshomeostasis might lead to neuronal malfunction prior to the death of neurons and the alteration of neuronal networks. In the present paper, we explore some of the molecular mechanisms underlying brain malfunction triggered by cerebrovascular disease and risk factors. We suggest that, in the age of genetic investigation and molecular diagnosis, the concept of vascular dementia needs a new approach.

Cross talk between activation of microglia and astrocytes in pathological conditions in the central nervous system

Microglia and astrocytes in the central nervous system are now recognized as active participants in various pathological conditions such as trauma, stroke, or chronic neurodegenerative disorders. Their activation is closely related with the development and severity of diseases. Interestingly, activation of microglia and astrocytes occurs with a spatially and temporarily distinct pattern. The present review explores the cross talk in the process of their activation. Microglia, activated earlier than astrocytes, promote astrocytic activation. On the other hand, activated astrocytes not only facilitate activation of distant microglia, but also inhibit microglial activities. Molecules contributing to their intercommunication include interleukin-1 (IL-1), adenosine triphosphate (ATP), and transforming growth factor beta (TGF-β). A better understanding about the cross talk between activation of microglia and astrocytes would be helpful to elucidate the role of glial cells in pathological conditions, which could accelerate the development of treatment for various diseases.

γ-Secretase component presenilin is important for microglia β-amyloid clearance

OBJECTIVE

The cleavage of amyloid precursor protein by γ-secretase is an important aspect of the pathogenesis of Alzheimer's disease. γ-Secretase also cleaves other membrane proteins (eg, Notch), which control cell development and homeostasis. Presenilin 1 and 2 are considered important determinants of the γ-secretase catalytic site. Our aim was to investigate whether γ-secretase can be important for microglial phagocytosis of Alzheimer's disease β-amyloid.

METHODS

We investigated the role of γ-secretase in microglia activity toward β-amyloid phagocytosis in cell culture using γ-secretase inhibitors and small hairpin RNA and presenilin-deficient mice.

RESULTS

We found that γ-secretase inhibitors impair microglial activity as measured in gene expression, protein levels, and migration ability, which resulted in a reduction of soluble β-amyloid phagocytosis. Moreover, microglia deficient in presenilin 1 and 2 showed impairment in phagocytosis of soluble β-amyloid. Dysfunction in the γ-secretase catalytic site led to an impairment in clearing insoluble β-amyloid from brain sections taken from an Alzheimer's disease mouse model when compared to microglia from wild-type mice.

INTERPRETATION

We suggest for the first time, a dual role for γ-secretase in Alzheimer's disease. One role is the cleavage of the amyloid precursor protein for pathologic β-amyloid production and the other is to regulate microglia activity that is important for clearing neurotoxic β-amyloid deposits. Further studies of γ-secretase-mediated cellular pathways in microglia may provide useful insights into the development of Alzheimer's disease and other neurodegenerative diseases, providing future avenues for therapeutic intervention.

The neuroinflammatory hypothesis of delirium

Delirium is a neuropsychiatric syndrome characterized by a sudden and global impairment in consciousness, attention and cognition. It is particularly frequent in elderly subjects with medical or surgical conditions and is associated with short- and long-term adverse outcomes. The pathophysiology of delirium remains poorly understood as it involves complex multi-factorial dynamic interactions between a diversity of risk factors. Several conditions associated with delirium are characterized by activation of the inflammatory cascade with acute release of inflammatory mediators into the bloodstream. There is compelling evidence that acute peripheral inflammatory stimulation induces activation of brain parenchymal cells, expression of proinflammatory cytokines and inflammatory mediators in the central nervous system. These neuroinflammatory changes induce neuronal and synaptic dysfunction and subsequent neurobehavioural and cognitive symptoms. Furthermore, ageing and neurodegenerative disorders exaggerate microglial responses following stimulation by systemic immune stimuli such as peripheral inflammation and/or infection. In this review we explore the neuroinflammatory hypothesis of delirium based on recent evidence derived from animal and human studies.

Effects of immunomodulatory substances on phagocytosis of abeta(1-42) by human microglia

Glial activation and increased inflammation characterize neuropathology in Alzheimer's disease (AD). The aim was to develop a model for studying phagocytosis of beta-amyloid (Abeta) peptide by human microglia and to test effects thereupon by immunomodulatory substances. Human CHME3 microglia showed intracellular Abeta(1-42) colocalized with lysosome-associated membrane protein-2, indicating phagocytosis. This was increased by interferon-gamma, and to a lesser degree with Protollin, a proteosome-based adjuvant. Secretion of brain-derived neurotrophic factor (BDNF) was decreased by Abeta(1-42) and by interferon-gamma and interleukin-1beta. These cytokines, but not Abeta(1-42), stimulated interleukin-6 release. Microglia which phagocytosed Abeta(1-42) exhibited a higher degree of expression of interleukin-1 receptor type I and inducible nitric oxide synthase. In conclusion, we show that human microglia are able to phagocytose Abeta(1-42) and that this is associated with expression of inflammatory markers. Abeta(1-42) and interferon-gamma decreased BDNF secretion suggesting a new neuropathological role for Abeta(1-42) and the inflammation accompanying AD.

Inflammation as a potential mediator for the association between periodontal disease and Alzheimer's disease

Periodontal disease (PDD) is associated with increased risk of cardiovascular disease, cerebrovascular disease, and mortality in many studies, while other studies have begun to suggest an association of PDD with Alzheimer's disease (AD). This paper discusses how infectious pathogens and systemic infection may play a role in AD. The roles of infection and inflammation are addressed specifically with regard to known AD pathologic lesions including senile plaques, neuron death, neurofibrillary tangles, and cerebrovascular changes. A testable model of proposed pathways between periodontal infection and AD is presented including three possible mechanisms: a) direct effects of infectious pathogens, b) inflammatory response to pathogens, and c) the effects on vascular integrity. The role of gene polymorphisms is discussed, including apolipoprotein (APOE) varepsilon4 as a pro-inflammatory and pro-infection genotype.

CD45RB is a novel molecular therapeutic target to inhibit Abeta peptide-induced microglial MAPK activation

Background

Microglial activation, characterized by p38 MAPK or p44/42 MAPK pathway signal transduction, occurs in Alzheimer's disease (AD). Our previous studies demonstrated CD45, a membrane-bound protein tyrosine phosphatase (PTP), opposed β-amyloid (Aβ) peptide-induced microglial activation via inhibition of p44/42 MAPK. Additionally we have shown agonism of the RB isoform of CD45 (CD45RB) abrogates lipopolysaccharide (LPS)-induced microglial activation.

Methodology and Results

In this study, CD45RB modulation of Aβ peptide or LPS-activated primary cultured microglial cells was further investigated. Microglial cells were co-treated with “aged” FITC-Aβ_1–42 and multiple CD45 isoform agonist antibodies. Data revealed cross-linking of CD45, particularly the CD45RB isoform, enhances microglial phagocytosis of Aβ_1–42 peptide and inhibits LPS-induced activation of p44/42 and p38 pathways. Co-treatment of microglial cells with agonist CD45 antibodies results in significant inhibition of LPS-induced microglial TNF-α and IL-6 release through p44/42 and/or p38 pathways. Moreover, inhibition of either of these pathways augmented CD45RB cross-linking induced microglial phagocytosis of Aβ_1–42 peptide. To investigate the mechanism(s) involved, microglial cells were co-treated with a PTP inhibitor (potassium bisperoxo [1,10-phenanthroline oxovanadate; Phen]) and Aβ_1–42 peptides. Data showed synergistic induction of microglial activation as evidenced by TNF-α and IL-6 release; both of which are demonstrated to be dependent on increased p44/42 and/or p38 activation. Finally, it was observed that cross-linking of CD45RB in the presence of Aβ_1–42 peptide, inhibits co-localization of microglial MHC class II and Aβ peptide; suggesting CD45 activation inhibits the antigen presenting phenotype of microglial cells.

Conclusion

In summary, p38 MAPK is another novel signaling pathway, besides p44/42, in which CD45RB cross-linking negatively regulates microglial Aβ phagocytosis while increasing potentially neurotoxic inflammation. Therefore, agonism of CD45RB PTP activity may be an effective therapeutic target for novel agents to treat AD due to its Aβ lowering, and inflammation reducing, properties that are particularly targeted at microglial cells. Such treatments may be more effective with less potential to produce systemic side-effects than therapeutics which induce non-specific, systemic down-regulation of inflammation.

Glial cell dysregulation: a new perspective on Alzheimer disease

Alzheimer disease (AD) is a major cause of dementia. Several mechanisms have been postulated to explain its pathogenesis, beta-amyloid (A beta toxicity, cholinergic dysfunction, Tau hyper-phosphorylation, oxidative damage, synaptic dysfunction and inflammation secondary to senile plaques, among others. Glial cells are the major producers of inflammatory mediators, and cytotoxic activation of glial cells is linked to several neurodegenerative diseases; however, whether inflammation is a consequence or the cause of neurodegeneration is still unclear. I propose that inflammation and cellular stress associated with aging are key events in the development of AD through the induction of glial dysfunction. Dysregulated inflammatory response can elicit glial cell activation by compounds which are normally poorly reactive. Inflammation can also be the major cause of defective handling of A beta and the amyloid precursor protein (APP). Here I review evidence that support the proposal that dysfunctional glia and the resulting neuroinflammation can explain many features of AD. Evidence supports the notion that damage caused by inflammation is not only a primary cause of neurodegeneration but also an inducer for the accumulation of A beta in AD. Dysfunctional glia can result in impaired neuronal function in AD, as well as in many progressive neurodegenerative disorders. We show that microglial cell activation is enhanced under pro-inflammatory conditions, indicating that glial cell responses to A beta related proteins can be critically dependent on the priming of glial cells by pro-inflammatory factors.