Microglial reactivity to β-amyloid is modulated by astrocytes and proinflammatory factors

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.

Encapsulated native and glucagon-like peptide-1 transfected human mesenchymal stem cells in a transgenic mouse model of Alzheimer's disease

Encapsulated human mesenchymal stem cells(MSC) are studied in a double transgenic mouse model of Alzheimer's disease (AD) after intraventricular implantation at 3 months of age. Abeta 40/42 deposition, and glial (GFAP) and microglial (CD11b) immunoreactivity were investigated 2 months after transplantation of either native MSC or MSC transfected with glucagon-like peptide-1 (GLP-1). CD11b immunostaining in the frontal lobes was significantly decreased in the GLP-1 MSC group compared to the untreated controls. Also, the plaque associated GFAP immunoreactivity was only observed in one of four animals in the GLP-1 MSC group. Abeta 40 whole brain ELISA was decreased in the MSC group: 86.06±5.2 pg/ml (untreated control) vs. 78.67±11.2 pg/ml (GLP-1 MSC group) vs.70.9±11.1 pg/ml (MSC group, p<0.05). Intraventricular transplantation of native and GLP-1 transfected MSC has been shown effective. Decreased amyloid deposition or suppression of glial and microglial responses were observed. However, encapsulation of MSC may alter their biological activity.

Autoantibodies to the adenosine triphosphate synthase play a pathogenetic role in Alzheimer's disease

It has become evident that an autoimmune component could play a role in Alzheimer's disease (AD) onset and/or progression. The aim of this study was to identify neuronal antigenic targets specifically recognized by serum autoantibodies and to investigate their cellular effects and their possible pathogenetic role. We identified, by an immunoproteomic approach using mouse brain proteins, the adenosine triphosphate (ATP) synthase β subunit as a new autoantigen in AD. Using an ELISA assay we found that serum anti-ATP synthase autoantibodies were present in 38% of patients with AD, but in no age-matched healthy subjects or in patients with Parkinson's disease or atherosclerosis. Analytical cytology studies, using SH-SY5Y neuroblastoma cell line, showed that ATP synthase autoantibodies were capable of inducing the inhibition of ATP synthesis, alterations of mitochondrial homeostasis and cell death by apoptosis. These findings suggest that autoantibodies specific to ATP synthase can exert a pathogenetic role via a mechanism that brings into play the impairment of the extracellular ATP homeostasis and the alteration of mitochondrial function triggering cell death by apoptosis.

Aging-dependent changes of microglial cells and their relevance for neurodegenerative disorders

Among multiple structural and functional brain changes, aging is accompanied by an increase of inflammatory signaling in the nervous system as well as a dysfunction of the immune system elsewhere. Although the long-held view that aging involves neurocognitive impairment is now dismissed, aging is a major risk factor for neurodegenerative diseases such as Alzheimer;s disease, Parkinson;s disease and Huntington's disease, among others. There are many age-related changes affecting the brain, contributing both to certain declining in function and increased frailty, which could singly and collectively affect neuronal viability and vulnerability. Among those changes, both inflammatory responses in aged brains and the altered regulation of toll like receptors, which appears to be relevant for understanding susceptibility to neurodegenerative processes, are linked to pathogenic mechanisms of several diseases. Here, we review how aging and pro-inflammatory environment could modulate microglial phenotype and its reactivity and contribute to the genesis of neurodegenerative processes. Data support our idea that age-related microglial cell changes, by inducing cytotoxicity in contrast to neuroprotection, could contribute to the onset of neurodegenerative changes. This view can have important implications for the development of new therapeutic approaches.

The role of astroglia in neuroprotection

Astrocytes are the main neural cell type responsible for the maintenance of brain homeostasis. They form highly organized anatomical domains that are interconnected into extensive networks. These features, along with the expression of a wide array of receptors, transporters, and ion channels, ideally position them to sense and dynamically modulate neuronal activity. Astrocytes cooperate with neurons on several levels, including neurotransmitter trafficking and recycling, ion homeostasis, energy metabolism, and defense against oxidative stress. The critical dependence of neurons upon their constant support confers astrocytes with intrinsic neuroprotective properties which are discussed here. Conversely, pathogenic stimuli may disturb astrocytic function, thus compromising neuronal functionality and viability. Using neuroinflammation, Alzheimer's disease, and hepatic encephalopathy as examples, we discuss how astrocytic defense mechanisms may be overwhelmed in pathological conditions, contributing to disease progression.

Inflammation in ALS and SMA: sorting out the good from the evil

Indices of neuroinflammation are found in a variety of diseases of the CNS including amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA). Over the years, neuroinflammation, in degenerative disorders of the CNS, has evolved from being regarded as an innocent bystander accomplishing its housekeeping function secondary to neurodegeneration to being considered as a bona fide contributor to the disease process and, in some situations, as a putative initiator of the disease. Herein, we will review neuroinflammation in both ALS and SMA not only from the angle of neuropathology but also from the angle of its potential role in the pathogenesis and treatment of these two dreadful paralytic disorders.

The multifaceted profile of activated microglia

Although relatively neglected previously, research efforts in the past decade or so have identified a pivotal role for glial cells in regulating neuronal function. Particular emphasis has been placed on increasing our understanding of the function of microglia because a change from the ramified "resting" state of these cells has been associated with the pathogenesis of several neurodegenerative diseases, notably Alzheimer's disease. However, it is not clear whether activation of microglia and the associated inflammatory changes play a part in triggering disease processes or whether cell activation is a response to the early changes associated with the disease. In either case, the possibility exists that modulation of microglial activation may be beneficial in some circumstances, underlying the need to pursue research in this area. The original morphological categorization of microglia by Del Rio Hortega into ameboid, ramified, and intermediate forms, must now be elaborated to encompass a functional description. The evidence which has been generated recently suggests that microglia are probably never in a "resting" state and that several intermediate transitional states, based on function and morphology, probably exist. A more complete understanding of these states and the triggers which lead to a change from one to another state, and the factors which modulate the molecular switch that determines the persistence of the "activated" state remain to be identified.

Proteomic Profiling of Cerebrospinal Fluid by 8-Plex iTRAQ Reveals Potential Biomarker Candidates of Alzheimer’s Disease

Introduction

Alzheimer’s disease (AD) poses specific challenges for drug development. It has a slow and variable clinical course, an insidious onset, and symptom expression is only observed when a significant proportion of neurons are already lost.

Discussion

Determinants of clinical course, such as molecular biomarkers, are urgently needed for early detection and diagnosis, or for prognosis and monitoring disease-modifying therapies in stratified patient populations. Due to its proximity to the brain and clinical availability, cerebrospinal fluid (CSF) is likely to have the highest yield of biomarker potential for neurodegenerative diseases. In this study, we examined the feasibility of using of an 8-plex isobaric tagging approach, coupled to two-dimensional liquid chromatography and tandem mass spectrometry using the matrix-assisted laser desorption/ionization time-of-flight/time-of-flight platform, for the discovery of potential biomarker candidates in CSF. Comparative analysis identified a number of statistically significant differences in the level of proteins when comparing AD to nondemented controls. Although the study is statistically underpowered to represent the disease population, the regulation of proteins with involvement in processes such as neuronal loss, synaptic dysfunction, neuroinflammation, and tissue degeneration and remodeling reflects the ability of our method in providing biologically meaningful CSF biomarkers as candidates for larger scale biomarker verification and validation studies.

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.

Microglial cells in astroglial cultures: a cautionary note

Primary rodent astroglial-enriched cultures are the most popular model to study astroglial biology in vitro. From the original methods described in the 1970's a great number of minor modifications have been incorporated into these protocols by different laboratories. These protocols result in cultures in which the astrocyte is the predominant cell type, but astrocytes are never 100% of cells in these preparations. The aim of this review is to bring attention to the presence of microglia in astroglial cultures because, in my opinion, the proportion of and the role that microglial cells play in astroglial cultures are often underestimated. The main problem with ignoring microglia in these cultures is that relatively minor amounts of microglia can be responsible for effects observed on cultures in which the astrocyte is the most abundant cell type. If the relative contributions of astrocytes and microglia are not properly assessed an observed effect can be erroneously attributed to the astrocytes. In order to illustrate this point the case of NO production in activated astroglial-enriched cultures is examined. Lipopolysaccharide (LPS) induces nitric oxide (NO) production in astroglial-enriched cultures and this effect is very often attributed to astrocytes. However, a careful review of the published data suggests that LPS-induced NO production in rodent astroglial-enriched cultures is likely to be mainly microglial in origin. This review considers cell culture protocol factors that can affect the proportion of microglial cells in astroglial cultures, strategies to minimize the proportion of microglia in these cultures, and specific markers that allow the determination of such microglial proportions.

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

Aberrant handling of Amyloid Precursor Protein (APP) and beta-amyloid (Abeta), glial activation and inflammation are key events in Alzheimer's disease. We set out to determine the role of inflammation on microglial reactivity against APP. We studied microglia-mediated neurotoxicity, uptake and degradation of a biotinylated APP construct (biotin-APP-C-244). APP, in contrast to Abeta, only induced mild activation of glial cells. However, under pro-inflammatory conditions, APP induced microglial-mediated cytotoxicity. Biotin-APP-C-244 or lipopolysaccharide and interferon-gamma (LPS+IFNgamma), administered separately, did not change reduction metabolism of microglia. However, biotin-APP-C-244+(LPS+IFNgamma) increased microglial reactivity and decreased reduction metabolism by 75% (P<0.001). Biotin-APP-C-244 was readily taken up by microglial cells; 80% was phagocytosed at 2 h. In the presence of LPS+IFNgamma, phagocytosis of biotin-APP-C-244 was reduced at 2 h; and cell damage was evident after 4 h. Our results support our hypothesis that, in neuroinflammation, microglial scavenger function is impaired and reactivity against APP enhanced as an initial step for neurodegeneration.

Modulation by astrocytes of microglial cell-mediated neuroinflammation: effect on the activation of microglial signaling pathways

The strong inflammatory response observed in neurodegenerative diseases can depend on the impairment of the endogenous control of microglial activation, triggering the release of potentially detrimental factors such as cytokines, nitric oxide (NO) and superoxide anion (O(2)(-)). Our aim was to study the activation of microglial cells and the transduction pathways involved in their modulation by IL-1beta and TNF-alpha. Microglial and mixed glial cell cultures from neonatal rats were exposed to IFN-gamma and/or IL-1beta and TNF-alpha. We analyzed NO secretion and the activation of ERK and STAT1. We found that astrocytes modulated microglial cell activation, decreasing production of NO. IFN-gamma induced an 18- to 25-fold increase in NO, associated to a 3- to 5-fold increase in ERK phosphorylation in microglial cultures. IL-1beta, but not TNF-alpha, inhibited IFN-gamma-induced production of NO in microglia by 87%. It also reduced IFN-gamma-induced phosphoERK (pERK) by 40%, without affecting phosphoSTAT1 (pSTAT1). In contrast, in microglial cultures exposed to media conditioned by astrocytes, IL-1beta did not inhibit pERK, whereas it reduced activation of STAT1. Inducible NO synthase expression induced by IFN-gamma in microglial cultures was reduced when the activation of ERK was prevented. We propose that IL-1beta modulates IFN-gamma-induced production of oxidative molecules through cross talk between STAT1 and MAPK pathways, regulating the amplitude and duration of microglial activation. Modulation of ERK was observed at 30 min, whereas inhibition of pSTAT was observed later (at 4 h), indicating that it was an early and transient phenomenon.

Cholinergic dysfunction, neuronal damage and axonal loss in TgCRND8 mice

In 7-month-old TgCRND8 mice, the extracellular cortical acetylcholine levels in vivo, the number and morphology of cholinergic neurons in the nucleus basalis magnocellularis and the ability to acquire an inhibitory avoidance response in the step-down test were studied. The TgCRND8 mouse brain is characterized by many beta-amyloid plaques, reduced neuronal and axonal staining, white matter demyelination, glia reaction and inducible nitric oxide synthase immunoreactivity. Choline acetyltransferase immunoreactivity in the nucleus basalis magnocellularis was significantly decreased. Basal and potassium-stimulated extracellular acetylcholine levels, investigated by microdialysis, and m2 muscarinic receptor immunoreactivity were reduced in the cortex of TgCRND8 mice, and scopolamine administration increased cortical extracellular acetylcholine levels in control but not in TgCRND8 mice. A cognitive impairment was demonstrated in the step-down test. These findings demonstrate that neuronal damage and cholinergic dysfunction in vivo underlie the impairment in learning and memory functions in this mouse model of Alzheimer's disease.

Complexity of astrocyte-motor neuron interactions in amyotrophic lateral sclerosis

Neurons and surrounding glial cells compose a highly specialized functional unit. In amyotrophic lateral sclerosis (ALS) astrocytes interact with motor neurons in a complex manner to modulate neuronal survival. Experiments using chimeric mice expressing ALS-linked mutations to Cu,Zn superoxide dismutase (SOD-1) suggest a critical modulation exerted by neighboring non-neuronal cell types on disease phenotype. When perturbed by primary neuronal damage, e.g. expression of SOD-1 mutations, neurons can signal astrocytes to proliferate and become reactive. Fibroblast growth factor-1 (FGF-1) can be released by motor neurons in response to damage to induce astrocyte activation by signaling through the receptor FGFR1. FGF-1 stimulates nerve growth factor (NGF) expression and secretion, as well as activity of the nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factor. Nrf2 leads to the expression of antioxidant and cytoprotective enzymes such as heme oxygenase-1 and a group of enzymes involved in glutathione metabolism that prevent motor neuron degeneration. However, prolonged stimulation with FGF-1 or SOD-mediated oxidative stress in astrocytes may disrupt the normal neuron-glia interactions and lead to progressive neuronal degeneration. The re-expression of p75 neurotrophin receptor and neuronal NOS in motor neurons in parallel with increased NGF secretion by reactive astrocytes may be a mechanism to eliminate critically damaged neurons. Consequently, astrocyte activation in ALS may have a complex pathogenic role.

Comparative study of microglia activation induced by amyloid-beta and prion peptides: Role in neurodegeneration

The inflammatory responses in Alzheimer's disease (AD) and prion-related encephalopathies (PRE) are dominated by microglia activation. Several studies have reported that the amyloid-beta (Abeta) peptides, which are associated with AD, and the pathogenic isoform of prion protein (PrPSc) have a crucial role in neuronal death and gliosis that occur in both of these disorders. In this study, we investigate whether Abeta and PrPSc cause microglia activation per se and whether these amyloidogenic peptides differentially affect these immunoeffector cells. In addition, we also determined whether substances released by Abeta- and PrP-activated microglia induce neuronal death. Cultures of rat brain microglia cells were treated with the synthetic peptides Abeta1-40, Abeta1-42 and PrP106-126 for different time periods. The lipopolysaccharide was used as a positive control of microglia activation. Our results show that Abeta1-40 and PrP106-126 caused similar morphological changes in microglia and increased the production of nitric oxide and hydroperoxides. An increase on inducible nitric oxide synthase expression was also observed in microglia treated with Abeta1-40 or PrP106. However, these peptides affected in a different manner the secretion of interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) secretion. In cocultures of microglia-neurons, it was observed that microglia treated with Abeta1-40 or PrP106-126 induced a comparable extent of neuronal death. The neutralizing antibody for IL-6 significantly reduced the neuronal death induced by Abeta- or PrP-activated microglia. Taken together, the data indicate that Abeta and PrP peptides caused microglia activation and differentially affected cytokine secretion. The IL-6 released by reactive microglia caused neuronal injury.

Clinical aspects of inflammation in Alzheimer's disease

In Alzheimer's disease (AD) there is increasing evidence that neurotoxicity is mediated by CNS inflammatory processes. These processes involve activation of microglia by amyloid-beta leading to release of pro-inflammatory cytokines including IL-1beta, IL-6, and TNF-alpha among others. Neurotoxic processes mediated by these cytokines may include direct neuronal death by enhancement of apoptosis, decreased synaptic function as evidence by inhibition of long-term potentiation, and inhibition of hippocampal neurogenesis. Central nervous system (CNS) inflammation may predate the development of senile plaques and neurofibrillary tangles in AD and may prove to be a more sensitive marker of prodromal AD. New developments in measuring CNS inflammation include measuring cytokine release by peripheral blood mononuclear cells and the development of PET markers of microglial activation. There is epidemiological evidence that circulating serum IL-6 is associated with poorer cognition. While epidemiological studies suggest a protective effect of NSAIDs against development of AD, controlled trials of NSAIDs to date have not shown any protective effect of drug. New anti-inflammatory agents for treating or preventing AD may include novel NSAIDs and opioid antagonists. These developments provide an alternative or potential adjunct to anti-amyloid therapies for AD.

Pro- and anti-inflammatory cytokines regulate the ERK pathway: Implication of the timing for the activation of microglial cells

Pro-inflammatory molecules induce glial activation and the release of potentially detrimental factors capable of generating oxidative damage, such as nitric oxide (NO) and superoxide anion (O2.-). Activated glial cells (astrocytes and microglia) are associated to the inflammatory process in neurodegenerative diseases. A strong inflammatory response could escape endogenous control becoming toxic to neurons and contributing to the course of the disease. We evaluated in a hippocampal cells-microglia co-culture model, if the pro-inflammatory condition induced by lipopolysaccharide + interferon-gamma (LPS+IFN-gamma) promoted damage directly or if damage was secondary to glial activation. In addition, we explored the effect of the anti-inflammatory cytokine transforming growth factor-beta1 (TGF-beta1), and pro-inflammatory cytokines, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) on the regulation of the inflammatory response of microglia. We found that LPS+IFN-gamma-induced damage on hippocampal cultures was dependent on the presence of microglial cells. In hippocampal cultures exposed to LPS+IFN-gamma, TGF-beta1 was induced whereas in microglial cell cultures LPS+IFN-gamma induced the secretion of IL-1beta. TGF-beta1 and IL-1beta but not TNF-alpha decreased the NO production by 70-90%. PD98059, an inhibitor of MAP kinase (MEK), reduced the IFN-gamma-induced NO production by 40%. TGF-beta and IL-1beta reduced the IFN-gamma induced phosphorylation of ERK1,2 by 60% and 40%, respectively. However, the effect of IL-1beta was observed at 30 min and that of TGF-beta1 only after 24 h of exposure. We propose that acting with different timing, TGF-beta1 and IL-1beta can modulate the extracellular signal-regulated kinase ERK1,2, as a common element for different transduction pathways, regulating the amplitude and duration of glial activation in response to LPS+IFN-gamma. Cross-talk among brain cells may be key for the understanding of inflammatory mechanisms involved in pathogenesis of neurodegenerative diseases.

AP-1 mediates beta-amyloid-induced iNOS expression in PC12 cells via the ERK2 and p38 MAPK signaling pathways

Nitrosative stress with subsequent inflammatory cell death has been implicated in some neurodegenerative disorders such as Alzheimer's disease (AD). Expression of inducible nitric oxide synthase (iNOS) and production of nitric oxide (NO) have been frequently elevated in AD. In this study, we have investigated the molecular mechanisms underlying nitrosative stress induced by beta-amyloid (A beta), a neurotoxic peptide associated with senile plaques formed in the brains of patients with AD. Exposure of rat pheochromocytoma (PC12) cells to the A beta resulted in increased mRNA and protein expression of iNOS and generation of NO. NO can rapidly interact with superoxide anion, forming more reactive peroxynitrite. Treatment of PC12 cells with A beta led to increased peroxynitrite production and nitrotyrosine formation. A beta induced activation of redox sensitive transcription factor activator protein-1 (AP-1), and AP-1 antisense oligonucleotide abolished the A beta-induced iNOS expression. Moreover, A beta transiently activated extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38 MAPK) via phosphorylation. Pharmacologic inhibition of both enzymes or dominant-negative mutation of ERK2 or p38 MAPK effectively down-regulated DNA binding as well as transcriptional activity of AP-1 and subsequent iNOS expression and NO production. The above findings suggest that A beta induces iNOS expression in PC12 cells through activation of AP-1 which is regulated by upstream kinases, such as ERK and p38 MAPK.

Expression of scavenger receptors in glial cells. Comparing the adhesion of astrocytes and microglia from neonatal rats to surface-bound beta-amyloid

Astrocytes and microglia associate to amyloid plaques, a pathological hallmark of Alzheimer disease. Microglia are activated by and can phagocytose beta-amyloid (Abeta). Scavenger receptors (SRs) are among the receptors mediating the uptake of fibrillar Abeta in vitro. However, little is known about the function of the astrocytes surrounding the plaques or the nature of their interaction with Abeta. It is unknown whether glial cells bind to nonfibrillar Abeta and if binding of astrocytes to Abeta depends on the same Scavenger receptors described for microglia. We determined the binding of glia to Abeta by an adhesion assay and evaluated the presence of scavenger receptors in glial cells by immunocytochemistry, immunohistochemistry of brain sections, and immunoblot. We found that astrocytes and microglia from neonatal rats adhered in a concentration-dependent manner to surfaces coated with fibrillar Abeta or nonfibrillar Abeta. Fucoidan and poly(I), known ligands for SR-type A, inhibited adhesion of microglia and astrocytes to Abeta and also inhibited Abeta phagocytosis. In contrast, a ligand for SR-type B like low density lipoprotein, did not compete glial adhesion to Abeta. Microglia presented immunodetectable SR-BI, SR-AI/AII, RAGE, and SR-MARCO (macrophage receptor with collagenous structure, a member of the SR-A family). Astrocytes presented SR-BI and SR-MARCO. To our knowledge, this is the first description of the presence of SR-MARCO in astrocytes. Our results indicate that both microglia and astrocytes adhere to fibrillar and nonfibrillar Abeta. Adhesion was mediated by a fucoidan-sensitive receptor. We propose that SR-MARCO could be the Scavenger receptor responsible for the adhesion of astrocytes and microglia to Abeta.

Protection of rat primary hippocampal cultures from Aβ cytotoxicity by pro-inflammatory molecules is mediated by astrocytes

The brain of Alzheimer's disease patients shows abundant dystrophic neurites in close proximity to fibrillar beta-amyloid (A beta) plaques, and activated glial cells. We evaluated the influence of pro-inflammatory molecules (LPS + IFN-gamma) on A beta(1-42) neurotoxicity. 2 microM A beta(1-42) induced apoptosis of hippocampal cells and LPS + IFN-gamma reduced the apoptosis induced by A beta. However, LPS + IFN-gamma prevented apoptosis only in hippocampal cultures containing astrocytes. Also, LPS + IFN-gamma induced the secretion of TGF beta, a cytokine having neuroprotective effects, only in hippocampal cultures that contained astrocytes. Astrocytes had a regulatory effect over microglial and neuronal responses to A beta. The results suggest that LPS + IFN-gamma, traditionally considered as pro-apoptotic, reduced apoptosis induced by A beta through the activation of neuroprotective mechanisms mediated by astrocytes. We propose that astrocytes are pivotal in the modulation of inflammation of the CNS. The impairment of the regulatory functions performed by activated astrocytes could represent an important pathogenic mechanism for neurodegenerative diseases.