Inflammation in Alzheimer disease-a brief review of the basic science and clinical literature

Sirtuin modulators control reactive gliosis in an in vitro model of Alzheimer's disease

Among neurodegenerative disorders, Alzheimer’s disease (AD) represents the most common cause of dementia in the elderly. Several genetic and environmental factors have been identified; however, aging represents the most important risk factor in the development of AD. To date, no effective treatments to prevent or slow this dementia are available. Sirtuins (SIRTs) are a family of NAD⁺-dependent enzymes, implicated in the control of a variety of biological processes that have the potential to modulate neurodegeneration. Here we tested the hypothesis that activation of SIRT1 or inhibition of SIRT2 would prevent reactive gliosis which is considered one of the most important hallmark of AD. Primary rat astrocytes were activated with beta amyloid 1-42 (Aβ 1-42) and treated with resveratrol (RSV) or AGK-2, a SIRT1 activator and a SIRT2-selective inhibitor, respectively. Results showed that both RSV and AGK-2 were able to reduce astrocyte activation as well as the production of pro-inflammatory mediators. These data disclose novel findings about the therapeutic potential of SIRT modulators, and suggest novel strategies for AD treatment.

Microglial phagocytosis of live neurons

Microglia, the brain's professional phagocytes, can remove dead and dying neurons as well as synapses and the processes of live neurons. However, we and others have recently shown that microglia can also execute neuronal death by phagocytosing stressed-but-viable neurons - a process that we have termed phagoptosis. In this Progress article, we discuss evidence suggesting that phagoptosis may contribute to neuronal loss during brain development, inflammation, ischaemia and neurodegeneration.

The involvement of lipids in Alzheimer's disease

It has been estimated that Alzheimer's disease (AD), the most common form of dementia, will affect approximately 81 million individuals by 2040. To date, the actual cause and cascade of events in the progression of this disease have not been fully determined. Furthermore, there is currently no definitive blood test or simple diagnostic method for AD. Considerable efforts have been put into proteomic approaches to develop a diagnostic blood test, but to date these efforts have not been successful. More recently, there has been a stronger focus on lipidomic studies in the hope of increasing our understanding of the underlying mechanisms leading to AD and developing an AD blood test. It is well known that the strongest genetic risk factor for AD is the ε4 variant of apolipoprotein E (APOE). Evidence suggests that the ApoE protein, a major lipid transporter, plays a key role in the pathogenesis of AD, and its role in both normal and aberrant lipid metabolism warrants further extensive investigation. Here, we review ApoE-lipid interactions, as well as the roles that lipids may play in the pathogenesis of AD.

Is Alzheimer's disease a systemic disease?

Although Alzheimer's disease (AD) is the most common neurodegenerative disease, the etiology of AD is not well understood. In some cases, genetic factors explain AD risk, but a high percentage of late-onset AD is unexplained. The fact that AD is associated with a number of physical and systemic manifestations suggests that AD is a multifactorial disease that affects both the CNS and periphery. Interestingly, a common feature of many systemic processes linked to AD is involvement in energy metabolism. The goals of this review are to 1) explore the evidence that peripheral processes contribute to AD risk, 2) explore ways that AD modulates whole-body changes, and 3) discuss the role of genetics, mitochondria, and vascular mechanisms as underlying factors that could mediate both central and peripheral manifestations of AD. Despite efforts to strictly define AD as a homogeneous CNS disease, there may be no single etiologic pathway leading to the syndrome of AD dementia. Rather, the neurodegenerative process may involve some degree of baseline genetic risk that is modified by external risk factors. Continued research into the diverse but related processes linked to AD risk is necessary for successful development of disease-modifying therapies.

Microglial dysfunction in brain aging and Alzheimer's disease

Microglia, the immune cells of the central nervous system, have long been a subject of study in the Alzheimer's disease (AD) field due to their dramatic responses to the pathophysiology of the disease. With several large-scale genetic studies in the past year implicating microglial molecules in AD, the potential significance of these cells has become more prominent than ever before. As a disease that is tightly linked to aging, it is perhaps not entirely surprising that microglia of the AD brain share some phenotypes with aging microglia. Yet the relative impacts of both conditions on microglia are less frequently considered in concert. Furthermore, microglial "activation" and "neuroinflammation" are commonly analyzed in studies of neurodegeneration but are somewhat ill-defined concepts that in fact encompass multiple cellular processes. In this review, we have enumerated six distinct functions of microglia and discuss the specific effects of both aging and AD. By calling attention to the commonalities of these two states, we hope to inspire new approaches for dissecting microglial mechanisms.

Building a pipeline to discover and validate novel therapeutic targets and lead compounds for Alzheimer's disease

Cognitive decline, Alzheimer's disease (AD) and other causes are major public health problems worldwide. With changing demographics, the number of persons with dementia will increase rapidly. The treatment and prevention of AD and other dementias, therefore, is an urgent unmet need. There have been considerable advances in understanding the biology of many age-related disorders that cause dementia. Gains in understanding AD have led to the development of ante-mortem biomarkers of traditional neuropathology and the conduct of several phase III interventions in the amyloid-β cascade early in the disease process. Many other intervention strategies are in various stages of development. However, efforts to date have met with limited success. A recent National Institute on Aging Research Summit led to a number of requests for applications. One was to establish multi-disciplinary teams of investigators who use systems biology approaches and stem cell technology to identify a new generation of AD targets. We were recently awarded one of three such grants to build a pipeline that integrates epidemiology, systems biology, and stem cell technology to discover and validate novel therapeutic targets and lead compounds for AD treatment and prevention. Here we describe the two cohorts that provide the data and biospecimens being exploited for our pipeline and describe the available unique datasets. Second, we present evidence in support of a chronic disease model of AD that informs our choice of phenotypes as the target outcome. Third, we provide an overview of our approach. Finally, we present the details of our planned drug discovery pipeline.

Impairment of in vivo calcium signaling in amyloid plaque-associated microglia

Neuroinflammation is a hallmark of Alzheimer's disease (AD) both in man and in multiple mouse models, and epidemiological studies link the use of anti-inflammatory drugs with a reduced risk of developing the disease. AD-related neuroinflammation is largely mediated by microglia, the main immune cells of the central nervous system. In vitro, executive functions of microglia are regulated by intracellular Ca(2+) signals, but little is known about microglial Ca(2+) signaling in vivo. Here we analyze in vivo properties of these cells in two mouse models of AD. In both strains plaque-associated microglia had hypertrophic/amoeboid morphology and were strongly positive for markers of activation such as CD11b and CD68. Activated microglia failed to respond reliably to extracellular release of adenosine triphosphate (ATP, mimicking tissue damage) and showed an increased incidence of spontaneous intracellular Ca(2+) transients. These Ca(2+) transients required activation of ATP receptors and Ca(2+) release from the intracellular Ca(2+) stores, and were not induced by neuronal or astrocytic hyperactivity. Neuronal silencing, however, selectively increased the frequency of Ca(2+) transients in plaque-associated microglia. Thus, our in vivo data reveal substantial dysfunction of plaque-associated microglia and identify a novel Ca(2+) signal possibly triggering a Ca(2+)-dependent release of toxic species in the plaque vicinity.

Hydroxy-safflor yellow A attenuates Aβ₁₋₄₂-induced inflammation by modulating the JAK2/STAT3/NF-κB pathway

Beta-amyloid (Aβ)-mediated inflammation plays a critical role in the initiation and progression of Alzheimer׳s disease (AD). Anti-inflammatory treatment may provide therapeutic benefits. In this study, the effect of hydroxy-safflor yellow A (HSYA) on Aβ1-42-induced inflammation in AD mice was investigated and the underlying mechanisms were explored. Aβ1-42 was injected into bilateral hippocampi of mice to induce AD models in vivo. Spatial learning and memory of mice were investigated by the Morris water maze test. Activated microglia and astrocytes were examined by immunofluorescence staining for ionized calcium-binding adapter molecule-1 (Iba-1) and glial fibrillary acidic protein (GFAP). The mRNA of inflammatory cytokines were measured using real-time PCR. NF-κB p65 translocation was analyzed by western blotting and immunostaining. IκB and phosphorylation of JAK2 and STAT3 were tested by western blotting. The results showed that HSYA ameliorated the memory deficits in Aβ1-42-induced AD mice. HSYA suppressed Aβ1-42-induced activation of microglia and astrocytes and reduced the mRNA expression of pro-inflammatory mediators. HSYA up-regulated the JAK2/STAT3 pathway and inhibits the activation of NF-κB signaling pathways. Pharmacological inhibition of STAT3 by AG490 reversed the inactivation of p65 and anti-inflammatory effects of HSYA. In conclusion, these results suggest that HSYA protects Aβ1-42-induced AD model through inhibiting inflammatory response, which may involve the JAK2/STAT3/NF-κB pathway.

Functional roles of p38 mitogen-activated protein kinase in macrophage-mediated inflammatory responses

Inflammation is a natural host defensive process that is largely regulated by macrophages during the innate immune response. Mitogen-activated protein kinases (MAPKs) are proline-directed serine and threonine protein kinases that regulate many physiological and pathophysiological cell responses. p38 MAPKs are key MAPKs involved in the production of inflammatory mediators, including tumor necrosis factor-α (TNF-α) and cyclooxygenase-2 (COX-2). p38 MAPK signaling plays an essential role in regulating cellular processes, especially inflammation. In this paper, we summarize the characteristics of p38 signaling in macrophage-mediated inflammation. In addition, we discuss the potential of using inhibitors targeting p38 expression in macrophages to treat inflammatory diseases.

Paraoxonase 1 in neurological disorders

Paroxonase 1 displays multiple physiological activities that position it as a putative player in the pathogenesis of neurological disorders. Here we reviewed the literature focusing on the role of paraoxonase 1 (PON1) as a factor in the risk of stroke and the major neurodegenerative diseases. PON1 activity is reduced in stroke patients, which significantly correlates inversely with carotid and cerebral atherosclerosis. The presence of the R allele of the Q192R PON1 polymorphism seems to potentiate this risk for stroke. PON1 exerts peroxidase activities that may be important in neurodegenerative disorders associated with oxidative stress. PON1 is also a key detoxifier of organophosphates and organophosphate exposure has been linked to the development of neurological disorders in which acetylcholine plays a significant role. In Parkinson's disease most of the studies suggest no participation of either L55M or the Q192R polymorphisms in its pathogenesis. However, many studies suggest that the MM55 PON1 genotype is associated with a higher risk for Parkinson's disease in individuals exposed to organophosphates. In Alzheimer's disease most studies have failed to find any association between PON1 polymorphisms and the development of the disease. Some studies show that PON1 activity is decreased in patients with Alzheimer's disease or other dementias, suggesting a possible protective role of PON1. No links between PON1 polymorphisms or activity have been found in other neurodegenerative diseases such as multiple sclerosis and amyotrophic lateral sclerosis. PON1 is a potential player in the pathogenesis of several neurological disorders. More research is warranted to ascertain the precise pathogenic links and the prognostic value of its measurement in neurological patients.

Methylene blue upregulates Nrf2/ARE genes and prevents tau-related neurotoxicity

Methylene blue (MB, methylthioninium chloride) is a phenothiazine that crosses the blood brain barrier and acts as a redox cycler. Among its beneficial properties are its abilities to act as an antioxidant, to reduce tau protein aggregation and to improve energy metabolism. These actions are of particular interest for the treatment of neurodegenerative diseases with tau protein aggregates known as tauopathies. The present study examined the effects of MB in the P301S mouse model of tauopathy. Both 4 mg/kg MB (low dose) and 40 mg/kg MB (high dose) were administered in the diet ad libitum from 1 to 10 months of age. We assessed behavior, tau pathology, oxidative damage, inflammation and numbers of mitochondria. MB improved the behavioral abnormalities and reduced tau pathology, inflammation and oxidative damage in the P301S mice. These beneficial effects were associated with increased expression of genes regulated by NF-E2-related factor 2 (Nrf2)/antioxidant response element (ARE), which play an important role in antioxidant defenses, preventing protein aggregation, and reducing inflammation. The activation of Nrf2/ARE genes is neuroprotective in other transgenic mouse models of neurodegenerative diseases and it appears to be an important mediator of the neuroprotective effects of MB in P301S mice. Moreover, we used Nrf2 knock out fibroblasts to show that the upregulation of Nrf2/ARE genes by MB is Nrf2 dependent and not due to secondary effects of the compound. These findings provide further evidence that MB has important neuroprotective effects that may be beneficial in the treatment of human neurodegenerative diseases with tau pathology.

High-fat diet-induced memory impairment in triple-transgenic Alzheimer's disease (3xTgAD) mice is independent of changes in amyloid and tau pathology

Obesity and consumption of a high-fat diet are known to increase the risk of Alzheimer's disease (AD). Diets high in fat also increase disease neuropathology and/or cognitive deficits in AD mouse models. However, the effect of a high-fat diet on both the neuropathology and memory impairments in the triple-transgenic mouse model of AD (3xTgAD) is unknown. Therefore, groups of 2-month-old male 3xTgAD and control (non-Tg) mice were maintained on a high-fat or control diet and memory was assessed at the age of 3-4, 7-8, 11-12, and 15-16 months using a series of behavioral tests. A comparable increase in body weight was observed in non-Tg and 3xTgAD mice after high-fat feeding at all ages tested but a significantly greater increase in epididymal adipose tissue was observed in 3xTgAD mice at the age of 7-8, 11-12, and 15-16 months. A high-fat diet caused memory impairments in non-Tg control mice as early as the age of 3-4 months. In 3xTgAD mice, high-fat consumption led to a reduction in the age of onset and an increase in the extent of memory impairments. Some of these effects of high-fat diet on cognition in non-Tg and 3xTgAD mice were transient, and the age at which cognitive impairment was detected depended on the behavioral test. The effect of high-fat diet on memory in the 3xTgAD mice was independent of changes in AD neuropathology as no significant differences in (plaques, oligomers) or tau neuropathology were observed. An acute increase in microglial activation was seen in high-fat fed 3xTgAD mice at the age of 3-4 months but in non-Tg control mice microglial activation was not observed until the age of 15-16 months. These data indicate therefore that a high-fat diet has rapid and long-lasting negative effects on memory in both control and AD mice that are associated with neuroinflammation, but independent of changes in beta amyloid and tau neuropathology in the AD mice.

Astrocyte-secreted matricellular proteins in CNS remodelling during development and disease

Matricellular proteins are secreted, nonstructural proteins that regulate the extracellular matrix (ECM) and interactions between cells through modulation of growth factor signaling, cell adhesion, migration, and proliferation. Despite being well described in the context of nonneuronal tissues, recent studies have revealed that these molecules may also play instrumental roles in central nervous system (CNS) development and diseases. In this minireview, we discuss the matricellular protein families SPARC (secreted protein acidic and rich in cysteine), Hevin/SC1 (SPARC-like 1), TN-C (Tenascin C), TSP (Thrombospondin), and CCN (CYR61/CTGF/NOV), which are secreted by astrocytes during development. These proteins exhibit a reduced expression in adult CNS but are upregulated in reactive astrocytes following injury or disease, where they are well placed to modulate the repair processes such as tissue remodeling, axon regeneration, glial scar formation, angiogenesis, and rewiring of neural circuitry. Conversely, their reexpression in reactive astrocytes may also lead to detrimental effects and promote the progression of neurodegenerative diseases.

Therapeutic implications of the prostaglandin pathway in Alzheimer's disease

An important pathologic hallmark of Alzheimer's disease (AD) is neuroinflammation, a process characterized in AD by disproportionate activation of cells (microglia and astrocytes, primarily) of the non-specific innate immune system within the CNS. While inflammation itself is not intrinsically detrimental, a delicate balance of pro- and anti-inflammatory signals must be maintained to ensure that long-term exaggerated responses do not damage the brain over time. Non-steroidal anti-inflammatory drugs (NSAIDs) represent a broad class of powerful therapeutics that temper inflammation by inhibiting cyclooxygenase-mediated signaling pathways including prostaglandins, which are the principal mediators of CNS neuroinflammation. While historically used to treat discrete or systemic inflammatory conditions, epidemiologic evidence suggests that protracted NSAID use may delay AD onset, as well as decrease disease severity and rate of progression. Unfortunately, clinical trials with NSAIDs have thus far yielded disappointing results, including premature discontinuation of a large-scale prevention trial due to unexpected cardiovascular side effects. Here we review the literature and make the argument that more targeted exploitation of downstream prostaglandin signaling pathways may offer significant therapeutic benefits for AD while minimizing adverse side effects. Directed strategies such as these may ultimately help to delay the deleterious consequences of brain aging and might someday lead to new therapies for AD and other chronic neurodegenerative diseases.

Sustained Na+/H+ exchanger activation promotes gliotransmitter release from reactive hippocampal astrocytes following oxygen-glucose deprivation

Hypoxia ischemia (HI)-related brain injury is the major cause of long-term morbidity in neonates. One characteristic hallmark of neonatal HI is the development of reactive astrogliosis in the hippocampus. However, the impact of reactive astrogliosis in hippocampal damage after neonatal HI is not fully understood. In the current study, we investigated the role of Na⁺/H⁺ exchanger isoform 1 (NHE1) protein in mouse reactive hippocampal astrocyte function in an in vitro ischemia model (oxygen/glucose deprivation and reoxygenation, OGD/REOX). 2 h OGD significantly increased NHE1 protein expression and NHE1-mediated H⁺ efflux in hippocampal astrocytes. NHE1 activity remained stimulated during 1–5 h REOX and returned to the basal level at 24 h REOX. NHE1 activation in hippocampal astrocytes resulted in intracellular Na⁺ and Ca²⁺ overload. The latter was mediated by reversal of Na⁺/Ca²⁺ exchange. Hippocampal astrocytes also exhibited a robust release of gliotransmitters (glutamate and pro-inflammatory cytokines IL-6 and TNFα) during 1–24 h REOX. Interestingly, inhibition of NHE1 activity with its potent inhibitor HOE 642 not only reduced Na⁺ overload but also gliotransmitter release from hippocampal astrocytes. The noncompetitive excitatory amino acid transporter inhibitor TBOA showed a similar effect on blocking the glutamate release. Taken together, we concluded that NHE1 plays an essential role in maintaining H⁺ homeostasis in hippocampal astrocytes. Over-stimulation of NHE1 activity following in vitro ischemia disrupts Na⁺ and Ca²⁺ homeostasis, which reduces Na⁺-dependent glutamate uptake and promotes release of glutamate and cytokines from reactive astrocytes. Therefore, blocking sustained NHE1 activation in reactive astrocytes may provide neuroprotection following HI.

Total body 100-mGy X-irradiation does not induce Alzheimer's disease-like pathogenesis or memory impairment in mice

The cause and progression of Alzheimer's disease (AD) are poorly understood. Possible cognitive and behavioral consequences induced by low-dose radiation are important because humans are exposed to ionizing radiation from various sources. Early transcriptional response in murine brain to low-dose X-rays (100 mGy) has been reported, suggesting alterations of molecular networks and pathways associated with cognitive functions, advanced aging and AD. To investigate acute and late transcriptional, pathological and cognitive consequences of low-dose radiation, we applied an acute dose of 100-mGy total body irradiation (TBI) with X-rays to C57BL/6J Jms mice. We collected hippocampi and analyzed expression of 84 AD-related genes. Mouse learning ability and memory were assessed with the Morris water maze test. We performed in vivo PET scans with (11)C-PIB, a radiolabeled ligand for amyloid imaging, to detect fibrillary amyloid beta peptide (Aβ) accumulation, and examined characteristic AD pathologies with immunohistochemical staining of amyloid precursor protein (APP), Aβ, tau and phosphorylated tau (p-tau). mRNA studies showed significant downregulation of only two of 84 AD-related genes, Apbb1 and Lrp1, at 4 h after irradiation, and of only one gene, Il1α, at 1 year after irradiation. Spatial learning ability and memory were not significantly affected at 1 or 2 years after irradiation. No induction of amyloid fibrillogenesis or changes in APP, Aβ, tau, or p-tau expression was detected at 4 months or 2 years after irradiation. TBI induced early or late transcriptional alteration in only a few AD-related genes but did not significantly affect spatial learning, memory or AD-like pathological change in mice.

Early administration of RS 67333, a specific 5-HT4 receptor agonist, prevents amyloidogenesis and behavioral deficits in the 5XFAD mouse model of Alzheimer's disease

Amyloid β (Aβ) accumulation is considered the main culprit in the pathogenesis of Alzheimer’s disease (AD). Recent studies suggest that decreasing Aβ production at very early stages of AD could be a promising strategy to slow down disease progression. Serotonin 5-HT₄ receptor activation stimulates α-cleavage of the amyloid precursor protein (APP), leading to the release of the soluble and neurotrophic sAPPα fragment and thus precluding Aβ formation. Using the 5XFAD mouse model of AD that shows accelerated Aβ deposition, we investigated the effect of chronic treatments (treatment onset at different ages and different durations) with the 5-HT₄ receptor agonist RS 67333 during the asymptomatic phase of the disease. Chronic administration of RS 67333 decreased concomitantly the number of amyloid plaques and the level of Aβ species. Reduction of Aβ levels was accompanied by a striking decrease in hippocampal astrogliosis and microgliosis. RS 67333 also transiently increased sAPPα concentration in the cerebrospinal fluid and brain. Moreover, a specific 5-HT₄ receptor antagonist (RS 39604) prevented the RS 67333-mediated reduction of the amyloid pathology. Finally, the novel object recognition test deficits of 5XFAD mice were reversed by chronic treatment with RS 67333. Collectively, these results strongly highlight this 5-HT₄ receptor agonist as a promising disease modifying-agent for AD.

The resolution of neuroinflammation in neurodegeneration: leukocyte recruitment via the choroid plexus

Inflammation is an integral part of the body's physiological repair mechanism, unless it remains unresolved and becomes pathological, as evident in the progressive nature of neurodegeneration. Based on studies from outside the central nervous system (CNS), it is now understood that the resolution of inflammation is an active process, which is dependent on well-orchestrated innate and adaptive immune responses. Due to the immunologically privileged status of the CNS, such resolution mechanism has been mostly ignored. Here, we discuss resolution of neuroinflammation as a process that depends on a network of immune cells operating in a tightly regulated sequence, involving the brain's choroid plexus (CP), a unique neuro-immunological interface, positioned to integrate signals it receives from the CNS parenchyma with signals coming from circulating immune cells, and to function as an on-alert gate for selective recruitment of inflammation-resolving leukocytes to the inflamed CNS parenchyma. Finally, we propose that functional dysregulation of the CP reflects a common underlying mechanism in the pathophysiology of neurodegenerative diseases, and can thus serve as a potential novel target for therapy.

High ferritin levels have major effects on the morphology of erythrocytes in Alzheimer's disease

Introduction: Unliganded iron both contributes to the pathology of Alzheimer's disease (AD) and also changes the morphology of erythrocytes (RBCs). We tested the hypothesis that these two facts might be linked, i.e., that the RBCs of AD individuals have a variant morphology, that might have diagnostic or prognostic value.

Methods: We included a literature survey of AD and its relationships to the vascular system, followed by a laboratory study. Four different microscopy techniques were used and results statistically compared to analyze trends between high and normal serum ferritin (SF) AD individuals.

Results: Light and scanning electron microscopies showed little difference between the morphologies of RBCs taken from healthy individuals and from normal SF AD individuals. By contrast, there were substantial changes in the morphology of RBCs taken from high SF AD individuals. These differences were also observed using confocal microscopy and as a significantly greater membrane stiffness (measured using force-distance curves).

Conclusion: We argue that high ferritin levels may contribute to an accelerated pathology in AD. Our findings reinforce the importance of (unliganded) iron in AD, and suggest the possibility both of an early diagnosis and some means of treating or slowing down the progress of this disease.

Clustering of transcriptional profiles identifies changes to insulin signaling as an early event in a mouse model of Alzheimer's disease

Background

Alzheimer’s disease affects more than 35 million people worldwide but there is no known cure. Age is the strongest risk factor for Alzheimer’s disease but it is not clear how age-related changes impact the disease. Here, we used a mouse model of Alzheimer’s disease to identify age-specific changes that occur prior to and at the onset of traditional Alzheimer-related phenotypes including amyloid plaque formation. To identify these early events we used transcriptional profiling of mouse brains combined with computational approaches including singular value decomposition and hierarchical clustering.

Results

Our study identifies three key events in early stages of Alzheimer’s disease. First, the most important drivers of Alzheimer’s disease onset in these mice are age-specific changes. These include perturbations of the ribosome and oxidative phosphorylation pathways. Second, the earliest detectable disease-specific changes occur to genes commonly associated with the hypothalamic-adrenal-pituitary (HPA) axis. These include the down-regulation of genes relating to metabolism, depression and appetite. Finally, insulin signaling, in particular the down-regulation of the insulin receptor substrate 4 (Irs4) gene, may be an important event in the transition from age-related changes to Alzheimer’s disease specific-changes.

Conclusion

A combination of transcriptional profiling combined with computational analyses has uncovered novel features relevant to Alzheimer’s disease in a widely used mouse model and offers avenues for further exploration into early stages of AD.

Perspective on future role of biological markers in clinical therapy trials of Alzheimer's disease: a long-range point of view beyond 2020

Recent advances in understanding the molecular mechanisms underlying various paths toward the pathogenesis of Alzheimer's disease (AD) has begun to provide new insight for interventions to modify disease progression. The evolving knowledge gained from multidisciplinary basic research has begun to identify new concepts for treatments and distinct classes of therapeutic targets; as well as putative disease-modifying compounds that are now being tested in clinical trials. There is a mounting consensus that such disease modifying compounds and/or interventions are more likely to be effectively administered as early as possible in the cascade of pathogenic processes preceding and underlying the clinical expression of AD. The budding sentiment is that "treatments" need to be applied before various molecular mechanisms converge into an irreversible pathway leading to morphological, metabolic and functional alterations that characterize the pathophysiology of AD. In light of this, biological indicators of pathophysiological mechanisms are desired to chart and detect AD throughout the asymptomatic early molecular stages into the prodromal and early dementia phase. A major conceptual development in the clinical AD research field was the recent proposal of new diagnostic criteria, which specifically incorporate the use of biomarkers as defining criteria for preclinical stages of AD. This paradigm shift in AD definition, conceptualization, operationalization, detection and diagnosis represents novel fundamental opportunities for the modification of interventional trial designs. This perspective summarizes not only present knowledge regarding biological markers but also unresolved questions on the status of surrogate indicators for detection of the disease in asymptomatic people and diagnosis of AD.

Uptake of environmental toxicants by the locus ceruleus: a potential trigger for neurodegenerative, demyelinating and psychiatric disorders

BACKGROUND

Damage to the locus ceruleus, with a subsequent decrease of CNS noradrenaline, occurs in a wide range of neurodegenerative, demyelinating and psychiatric disorders. The cause of the initial locus ceruleus damage remains unknown. Recently, inorganic mercury was found to enter human locus ceruleus neurons selectively. This has led to the formulation of a new hypothesis as to the cause of these disorders.

HYPOTHESIS

Toxicants enter locus ceruleus neurons selectively, aided by the extensive exposure these neurons have to CNS capillaries, as well as by stressors that upregulate locus ceruleus activity. The resulting noradrenaline dysfunction affects a wide range of CNS cells and can trigger a number of neurodegenerative (Alzheimer's, Parkinson's and motor neuron disease), demyelinating (multiple sclerosis), and psychiatric (major depression and bipolar disorder) conditions.

CONCLUSIONS

This hypothesis proposes that environmental toxicants entering the locus ceruleus can give rise to a variety of CNS disorders. Proposals are made for experiments to gain further evidence for this hypothesis. If it is shown that toxicants in the locus ceruleus are responsible for these conditions, attempts can be made to prevent the toxicant exposures or to remove the toxicants from the nervous system.

In vivo modification of Abeta plaque toxicity as a novel neuroprotective lithium-mediated therapy for Alzheimer's disease pathology

Background

Alzheimer’s disease (AD) is characterized by the abnormal accumulation of extracellular beta-amyloid (Abeta) plaques, intracellular hyperphosphorylated tau, progressive synaptic alterations, axonal dystrophies, neuronal loss and the deterioration of cognitive capabilities of patients. However, no effective disease-modifying treatment has been yet developed. In this work we have evaluated whether chronic lithium treatment could ameliorate the neuropathology evolution of our well characterized PS1M146LxAPPSwe-London mice model.

Results

Though beneficial effects of lithium have been previously described in different AD models, here we report a novel in vivo action of this compound that efficiently ameliorated AD-like pathology progression and rescued memory impairments by reducing the toxicity of Abeta plaques. Transgenic PS1M146LxAPPSwe-London mice, treated before the pathology onset, developed smaller plaques characterized by higher Abeta compaction, reduced oligomeric-positive halo and therefore with attenuated capacity to induce neuronal damage. Importantly, neuronal loss in hippocampus and entorhinal cortex was fully prevented. Our data also demonstrated that the axonal dystrophic area associated with lithium-modified plaques was highly reduced. Moreover, a significant lower accumulation of phospho-tau, LC3-II and ubiquitinated proteins was detected in treated mice. Our study highlights that this switch of plaque quality by lithium could be mediated by astrocyte activation and the release of heat shock proteins, which concentrate in the core of the plaques.

Conclusions

Our data demonstrate that the pharmacological in vivo modulation of the extracellular Abeta plaque compaction/toxicity is indeed possible and, in addition, might constitute a novel promising and innovative approach to develop a disease-modifying therapeutic intervention against AD.

Loss of P2Y₂ nucleotide receptors enhances early pathology in the TgCRND8 mouse model of Alzheimer's disease

Neuroinflammation is a prominent feature in Alzheimer's disease (AD) and activation of the brain's innate immune system, particularly microglia, has been postulated to both retard and accelerate AD progression. Recent studies indicate that the G protein-coupled P2Y2 nucleotide receptor (P2Y2R) is an important regulator of innate immunity by assisting in the recruitment of monocytes to injured tissue, neutrophils to bacterial infections and eosinophils to allergen-infected lungs. In this study, we investigated the role of the P2Y2R in progression of an AD-like phenotype in the TgCRND8 mouse model that expresses Swedish and Indiana mutations in amyloid precursor protein (APP). Our results indicate that P2Y 2 R expression is upregulated in TgCRND8 mouse brain within 10 weeks of age and then decreases after 25 weeks of age, as compared to littermate controls expressing low levels of the P2Y 2 R. TgCRND8 mice with homozygous P2Y 2 R deletion survive less than 5 weeks, whereas mice with heterozygous P2Y 2 R deletion survive for 12 weeks, a time point when TgCRND8 mice are fully viable. Heterozygous P2Y 2 R deletion in TgCRND8 mice increased β-amyloid (Aβ) plaque load and soluble Aβ1-42 levels in the cerebral cortex and hippocampus, decreased the expression of the microglial marker CD11b in these brain regions and caused neurological deficits within 10 weeks of age, as compared to age-matched TgCRND8 mice. These findings suggest that the P2Y2R is important for the recruitment and activation of microglial cells in the TgCRND8 mouse brain and that the P2Y2R may regulate neuroprotective mechanisms through microglia-mediated clearance of Aβ that when lost can accelerate the onset of an AD-like phenotype in the TgCRND8 mouse.

Blocking the apolipoprotein E/amyloid β interaction in triple transgenic mice ameliorates Alzheimer's disease related amyloid β and tau pathology

Inheritance of the apolipoprotein E4 (apoE4) genotype has been identified as the major genetic risk factor for late-onset Alzheimer's disease (AD). Studies have shown that the binding between apoE and amyloid-β (Aβ) peptides occurs at residues 244-272 of apoE and residues 12-28 of Aβ. ApoE4 has been implicated in promoting Aβ deposition and impairing clearance of Aβ. We hypothesized that blocking the apoE/Aβ interaction would serve as an effective new approach to AD therapy. We have previously shown that treatment with Aβ12-28P can reduce amyloid plaques in APP/PS1 transgenic (Tg) mice and vascular amyloid in TgSwDI mice with congophilic amyloid angiopathy. In the present study, we investigated whether the Aβ12-28P elicits a therapeutic effect on tau-related pathology in addition to amyloid pathology using old triple transgenic AD mice (3xTg, with PS1M146V , APPSwe and tauP30IL transgenes) with established pathology from the ages of 21 to 26 months. We show that treatment with Aβ12-28P substantially reduces tau pathology both immunohistochemically and biochemically, as well as reducing the amyloid burden and suppressing the activation of astrocytes and microglia. These affects correlate with a behavioral amelioration in the treated Tg mice.

The role of iron-induced fibrin in the pathogenesis of Alzheimer's disease and the protective role of magnesium

Amyloid hypothesis of Alzheimer's disease (AD) has recently been challenged by the increasing evidence for the role of vascular and hemostatic components that impair oxygen delivery to the brain. One such component is fibrin clots, which, when they become resistant to thrombolysis, can cause chronic inflammation. It is not known, however, why some cerebral thrombi are resistant to the fibrinolytic degradation, whereas fibrin clots formed at the site of vessel wall injuries are completely, although gradually, removed to ensure proper wound healing. This phenomenon can now be explained in terms of the iron-induced free radicals that generate fibrin-like polymers remarkably resistant to the proteolytic degradation. It should be noted that similar insoluble deposits are present in AD brains in the form of aggregates with Abeta peptides that are resistant to fibrinolytic degradation. In addition, iron-induced fibrin fibers can irreversibly trap red blood cells (RBCs) and in this way obstruct oxygen delivery to the brain and induce chronic hypoxia that may contribute to AD. The RBC-fibrin aggregates can be disaggregated by magnesium ions and can also be prevented by certain polyphenols that are known to have beneficial effects in AD. In conclusion, we argue that AD can be prevented by: (1) limiting the dietary supply of trivalent iron contained in red and processed meat; (2) increasing the intake of chlorophyll-derived magnesium; and (3) consumption of foods rich in polyphenolic substances and certain aliphatic and aromatic unsaturated compounds. These dietary components are present in the Mediterranean diet known to be associated with the lower incidence of AD and other degenerative diseases.

Beyond amyloid: getting real about nonamyloid targets in Alzheimer's disease

For decades, researchers have focused primarily on a pathway initiated by amyloid beta aggregation, amyloid deposition, and accumulation in the brain as the key mechanism underlying the disease and the most important treatment target. However, evidence increasingly suggests that amyloid is deposited early during the course of disease, even prior to the onset of clinical symptoms. Thus, targeting amyloid in patients with mild to moderate Alzheimer's disease (AD), as past failed clinical trials have done, may be insufficient to halt further disease progression. Scientists are investigating other molecular and cellular pathways and processes that contribute to AD pathogenesis. Thus, the Alzheimer's Association's Research Roundtable convened a meeting in April 2012 to move beyond amyloid and explore AD as a complex multifactorial disease, with the goal of using a more inclusive perspective to identify novel treatment strategies.

Cerebrovascular reactivity to carbon dioxide in Alzheimer's disease

There is growing evidence that cerebrovascular reactivity to carbon dioxide (CVRCO2) is impaired in Alzheimer's disease (AD). Preclinical and animal studies suggest chronic hypercontractility in brain vessels in AD. We review (a) preclinical studies of mechanisms for impaired CVRCO2 in AD; (b) clinical studies of cerebrovascular function in subjects with AD dementia, mild cognitive impairment (MCI), and normal cognition. Although results of clinical studies are inconclusive, an increasing number of reports reveal an impairment of vascular reactivity to carbon dioxide in subjects with AD, and possibly also in MCI. Thus, CVRCO2 may be an attractive means to detect an early vascular dysfunction in subjects at risk.

Studying the role of ApoE in Alzheimer's disease pathogenesis using a systems biology model

Alzheimer's disease (AD) is the most common form of dementia. Even with its well-known symptoms of memory loss and well-characterized pathology of beta amyloid (Aβ) plaques and neurofibrillary tangles, the disease pathogenesis and initiating factors are still not well understood. To tackle this problem, a systems biology model has been developed and used to study the varying effects of variations in the ApoE allele present, as well as the effects of short term and periodic inflammation at low to moderate levels. Simulations showed a late onset peak of Aβ in the ApoE4 case that lead to localized neuron loss which could be ameliorated in part by application of short-term pro-inflammatory mediators. The model that has been developed herein represents one of the first attempts to model AD from a systems approach to study physiologically relevant parameters that may prove useful to physicians in the future.

Isoorientin attenuates lipopolysaccharide-induced pro-inflammatory responses through down-regulation of ROS-related MAPK/NF-κB signaling pathway in BV-2 microglia

Isoorientin (ISO) is a flavonoid compound in the human diet, and has been known to possess various bioactivities. However, the effects of ISO on microglia inflammation have not been investigated. The current study investigates the neuroprotective effect of ISO in LPS-activated mouse microglial (BV-2) cells. ISO significantly increased the BV-2 cells viability, blocked the protein expression of inducible nitric oxide synthase and cyclooxygenase-2, and decreased the production of nitric oxide, pro-inflammatory cytokines including tumor necrosis factor-α and interleukin-1β. The activation of mitogen-activated protein kinases (MAPKs) was blocked by ISO, and NF-κB nuclear translocation was decreased by ISO both alone and together with NF-κB inhibitor (PDTC) and MAPKs inhibitors (U0126, SP 600125, and SB 203580). Furthermore, ISO strongly quenched intracellular reactive oxygen species (ROS) generation. ROS inhibitor (N-acetyl cysteine, NAC) significantly inhibited pro-inflammatory cytokines release and NF-κB and MAPKs activation, indicating that ISO attenuated neuroinflammation by inhibiting the ROS-related MAPK/NF-κB signaling pathway.

Negative regulation of TLX by IL-1β correlates with an inhibition of adult hippocampal neural precursor cell proliferation

Adult hippocampal neurogenesis is modulated by a number of intrinsic and extrinsic factors including local signalling molecules, exercise, aging and inflammation. Inflammation is also a major contributor to several hippocampal-associated disorders. Interleukin-1beta (IL-1β) is the most predominant pro-inflammatory cytokine in the brain, and an increase in its concentration is known to decrease the proliferation of both embryonic and adult hippocampal neural precursor cells (NPCs). Recent research has focused on the role of nuclear receptors as intrinsic regulators of neurogenesis, and it is now established that the orphan nuclear receptor TLX is crucial in maintaining the NPC pool in neurogenic brain regions. To better understand the involvement of TLX in IL-1β-mediated effects on hippocampal NPC proliferation, we examined hippocampal NPC proliferation and TLX expression in response to IL-1β treatment in an adult rat hippocampal neurosphere culture system. We demonstrate that IL-1β reduced the proliferation of hippocampal NPCs and TLX expression in a dose and time-dependent manner and that co-treatment with IL-1β receptor antagonist or IL-1 receptor siRNA prevented these effects. We also report a dose-dependent effect of IL-1β on the composition of cell phenotypes in the culture and on expression of TLX in these cells. This study thus provides evidence of an involvement of TLX in IL-1β-induced changes in adult hippocampal neurogenesis, and offers mechanistic insight into disorders in which neuroinflammation and alterations in neurogenesis are characteristic features.

1α,25-dihydroxyvitamin D3 and resolvin D1 retune the balance between amyloid-β phagocytosis and inflammation in Alzheimer's disease patients

As immune defects in amyloid-β (Aβ) phagocytosis and degradation underlie Aβ deposition and inflammation in Alzheimer's disease (AD) brain, better understanding of the relation between Aβ phagocytosis and inflammation could lead to promising preventive strategies. We tested two immune modulators in peripheral blood mononuclear cells (PBMCs) of AD patients and controls: 1α,25(OH)2-vitamin D3 (1,25D3) and resolvin D1 (RvD1). Both 1,25D3 and RvD1 improved phagocytosis of FAM-Aβ by AD macrophages and inhibited fibrillar Aβ-induced apoptosis. The action of 1,25D3 depended on the nuclear vitamin D and the protein disulfide isomerase A3 receptors, whereas RvD1 required the chemokine receptor, GPR32. The activities of 1,25D3 and RvD1 commonly required intracellular calcium, MEK1/2, PKA, and PI3K signaling; however, the effect of RvD1 was more sensitive to pertussis toxin. In this case study, the AD patients: a) showed significant transcriptional up regulation of IL1RN, ITGB2, and NFκB; and b) revealed two distinct groups when compared to controls: group 1 decreased and group 2 increased transcription of TLRs, IL-1, IL1R1 and chemokines. In the PBMCs/macrophages of both groups, soluble Aβ (sAβ) increased the transcription/secretion of cytokines (e.g., IL1 and IL6) and chemokines (e.g., CCLs and CXCLs) and 1,25D3/RvD1 reversed most of the sAβ effects. However, they both further increased the expression of IL1 in the group 1, sβ-treated cells. We conclude that in vitro, 1,25D3 and RvD1 rebalance inflammation to promote Aβ phagocytosis, and suggest that low vitamin D3 and docosahexaenoic acid intake and/or poor anabolic production of 1,25D3/RvD1 in PBMCs could contribute to AD onset/pathology.

Apolipoprotein E as a β-amyloid-independent factor in Alzheimer's disease

APOE, which encodes apolipoprotein E, is the most prevalent and best established genetic risk factor for late-onset Alzheimer’s disease. Current understanding of Alzheimer’s disease pathophysiology posits an important role for apolipoprotein E in the disease cascade via its interplay with β-amyloid. However, evidence is also emerging for roles of apolipoprotein E in the disease process that are independent of β-amyloid. Particular areas of interest are lipid metabolism, tau pathology, neuroenergetics, neurodevelopment, synaptic plasticity, the neurovasculature, and neuroinflammation. The intent of this article is to review the literature in each of these areas.

Intracerebroventricular streptozotocin exacerbates Alzheimer-like changes of 3xTg-AD mice

Alzheimer's disease (AD) involves several possible molecular mechanisms, including impaired brain insulin signaling and glucose metabolism. To investigate the role of metabolic insults in AD, we injected streptozotocin (STZ), a diabetogenic compound if used in the periphery, into the lateral ventricle of the 6-month-old 3xTg-AD mice and studied the cognitive function as well as AD-like brain abnormalities, such as tau phosphorylation and Aβ accumulation, 3-6 weeks later. We found that STZ exacerbated impairment of short-term and spatial reference memory in 3xTg-AD mice. We also observed an increase in tau hyperphosphorylation and neuroinflammation, a disturbance of brain insulin signaling, and a decrease in synaptic plasticity and amyloid β peptides in the brain after STZ treatment. The expression of 20 AD-related genes, including those involved in the processing of amyloid precursor protein, cytoskeleton, glucose metabolism, insulin signaling, synaptic function, protein kinases, and apoptosis, was altered, suggesting that STZ disturbs multiple metabolic and cell signaling pathways in the brain. These findings provide experimental evidence of the role of metabolic insult in AD.

SUMO and Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline and is the most common cause of dementia in the elderly. Histopathologically, AD features insoluble aggregates of two proteins in the brain, amyloid-β (Aβ) and the microtubule-associated protein tau, both of which have been linked to the small ubiquitin-like modifier (SUMO). A large body of research has elucidated many of the molecular and cellular pathways that underlie AD, including those involving the abnormal Aβ and tau aggregates. However, a full understanding of the etiology and pathogenesis of the disease has remained elusive. Consequently, there are currently no effective therapeutic options that can modify the disease progression and slow or stop the decline of cognitive functioning. As part of the effort to address this lacking, there needs a better understanding of the signaling pathways that become impaired under AD pathology, including the regulatory mechanisms that normally control those networks. One such mechanism involves SUMOylation, which is a post-translational modification (PTM) that is involved in regulating many aspects of cell biology and has also been found to have several critical neuron-specific roles. Early studies have indicated that the SUMO system is likely altered with AD-type pathology, which may impact Aβ levels and tau aggregation. Although still a relatively unexplored topic, SUMOylation will likely emerge as a significant factor in AD pathogenesis in ways which may be somewhat analogous to other regulatory PTMs such as phosphorylation. Thus, in addition to the upstream effects on tau and Aβ processing, there may also be downstream effects mediated by Aβ aggregates or other AD-related factors on SUMO-regulated signaling pathways. Multiple proteins that have functions relevant to AD pathology have been identified as SUMO substrates, including those involved in synaptic physiology, mitochondrial dynamics, and inflammatory signaling. Ongoing studies will determine how these SUMO-regulated functions in neurons and glial cells may be impacted by Aβ and AD pathology. Here, we present a review of the current literature on the involvement of SUMO in AD, as well as an overview of the SUMOylated proteins and pathways that are potentially dysregulated with AD pathogenesis.

Chronic airway-induced allergy in mice modifies gene expression in the brain toward insulin resistance and inflammatory responses

BACKGROUND

Chronic systemic inflammation affects brain functionality and may negatively influence the progression of neurodegenerative disorders. Allergy is a chronic inflammatory disease affecting more than 20% of the Western population. Little is known regarding the influence of allergy on brain functions. The aim of the present study was to obtain a global overview of the genes that drive the effects of peripheral inflammation associated with chronic airway-induced allergy in the brain.

METHODS

Airway allergy was induced in C57B/6J mice using ovalbumin as the allergen. Microarray analysis was performed in the hippocampus and frontal cortex in association with Affymetrix. For the data analysis, principal component analysis and orthogonal to latent structures discriminant analysis followed by pathway analysis were used. Quantitative polymerase chain reaction (qPCR) and protein analysis by Western blotting were performed for the validation of microarray results.

RESULTS

Microarray analysis showed low-grade changes in gene expression in the brain induced by airway-associated allergy. Changes in expression were observed for genes involved in antigen processing and presentation, cytokine-cytokine interaction, Toll-like receptor and mitogen-activated protein kinase signaling, as determined by pathway analysis. We confirmed a reduction of insulin-degrading enzyme at the protein level and a decrease in insulin receptor phosphorylation in the brains of allergic mice. Other allergy-induced gene expression changes were confirmed by qPCR, including increased levels of tumor necrosis factor receptor superfamily member 23 and lipopolysaccharide-binding protein.

CONCLUSION

Airway-associated allergy induces changes in brain gene expression toward induction of insulin resistance and inflammatory responses with potential implications for neurodegenerative disorders.

Microglia: a new frontier for synaptic plasticity, learning and memory, and neurodegenerative disease research

We focus on emerging roles for microglia in synaptic plasticity, cognition and disease. We outline evidence that ramified microglia, traditionally thought to be functionally "resting" (i.e. quiescent) in the normal brain, in fact are highly dynamic and plastic. Ramified microglia continually and rapidly extend processes, contact synapses in an activity and experience dependent manner, and play a functionally dynamic role in synaptic plasticity, possibly through release of cytokines and growth factors. Ramified microglial also contribute to structural plasticity through the elimination of synapses via phagocytic mechanisms, which is necessary for normal cognition. Microglia have numerous mechanisms to monitor neuronal activity and numerous mechanisms also exist to prevent them transitioning to an activated state, which involves retraction of their surveying processes. Based on the evidence, we suggest that maintaining the ramified state of microglia is essential for normal synaptic and structural plasticity that supports cognition. Further, we propose that change of their ramified morphology and function, as occurs in inflammation associated with numerous neurological disorders such as Alzheimer's and Parkinson's disease, disrupts their intricate and essential synaptic functions. In turn altered microglia function could cause synaptic dysfunction and excess synapse loss early in disease, initiating a range of pathologies that follow. We conclude that the future of learning and memory research depends on an understanding of the role of non-neuronal cells and that this should include using sophisticated molecular, cellular, physiological and behavioural approaches combined with imaging to causally link the role of microglia to brain function and disease including Alzheimer's and Parkinson's disease and other neuropsychiatric disorders.

Cellular and molecular mediators of neuroinflammation in the pathogenesis of Parkinson's disease

Neuroinflammation is a host-defense mechanism associated with restoration of normal structure and function of the brain and neutralization of an insult. Increasing neuropathological and biochemical evidence from the brains of individuals with Parkinson's disease (PD) provides strong evidence for activation of neuroinflammatory pathways. Microglia, the resident innate immune cells, may play a major role in the inflammatory process of the diseased brain of patients with PD. Although microglia forms the first line of defense for the neural parenchyma, uncontrolled activation of microglia may directly affect neurons by releasing various molecular mediators such as inflammatory cytokines (tumor necrosis factor-α, interleukin [IL]-6, and IL-1β), nitric oxide, prostaglandin E2, and reactive oxygen and nitrogen species. Moreover, recent studies have reported that activated microglia phagocytose not only damaged cell debris but also intact neighboring cells. This phenomenon further supports their active participation in self-enduring neuronal damage cycles. As the relationship between PD and neuroinflammation is being studied, there is a realization that both cellular and molecular mediators are most likely assisting pathological processes leading to disease progression. Here, we discuss mediators of neuroinflammation, which are known activators released from damaged parenchyma of the brain and result in neuronal degeneration in patients with PD.

Deciphering Alzheimer disease

Alzheimer disease represents an insidious impairment of intellect and emotional well-being. However, recent advances in biochemical pathology and human genetics offer promise that effective therapeutic agents may soon be developed.

Is there a causal link between inflammation and dementia?

Neuroinflammation is a constant event in Alzheimer's disease (AD), but the current knowledge is insufficient to state whether inflammation is a cause, a promoter, or simply a secondary phenomenon in this inexorably progressive ailment. In the current paper, we review research data showing that inflammation is not a prerequisite for onset of dementia, and, although it may worsen the course of the disease, recent evidence shows that chronic inhibition of inflammatory pathways is not necessarily beneficial for patients. Prospective clinical trials with anti-inflammatory drugs failed to stop disease progression, measurements of inflammatory markers in serum and cerebrospinal fluid of patients yielded contradictory results, and recent bench research proved undoubtedly that neuroinflammation has a protective side as well. Knockout animal models for TNFRs or ILRs do not seem to prevent the pathology or the cognitive decline, but quite the contrary. In AD, the therapeutic intervention on inflammatory pathways still has a research future, but its targets probably need reevaluation.

Tenascin-C deficiency ameliorates Alzheimer's disease-related pathology in mice

Alzheimer's disease (AD) is a neurodegenerative disease characterized by deposits of amyloid β peptide (Aβ) and microglia-driven inflammatory activation. Tenascin-C (tnc) is an extracellular matrix protein that is upregulated in inflammation and induces further inflammatory responses. We hypothesized that tnc contributes to the inflammatory pathology in AD. Using real-time polymerase chain reaction, we observed that tnc gene transcription was upregulated in cultured microglia after Aβ challenge and in the brain of an AD mouse model that overexpresses mutated amyloid precursor protein (APP) in neural cells. By cross-breeding APP-transgenic mice and tenascin-C-deficient mice, we demonstrated using real-time polymerase chain reaction, Western blot analysis, enzyme-linked immunosorbent assay, and immunohistochemistry that tnc deficiency reduces pro- but enhances anti-inflammatory activation in the mutated APP-transgenic mouse brain, associated with a reduced cerebral Aβ load and higher levels of the postsynaptic density protein 95. Thus, our study indicates that functional inhibition of tnc exerts beneficial effects on AD pathogenesis, suggesting a potential for tnc as a new therapeutic target in AD.

Up-regulation and activation of the P2Y(2) nucleotide receptor mediate neurite extension in IL-1β-treated mouse primary cortical neurons

The pro-inflammatory cytokine interleukin-1β (IL-1β), whose levels are elevated in the brain in Alzheimer's and other neurodegenerative diseases, has been shown to have both detrimental and beneficial effects on disease progression. In this article, we demonstrate that incubation of mouse primary cortical neurons (mPCNs) with IL-1β increases the expression of the P2Y2 nucleotide receptor (P2Y2R) and that activation of the up-regulated receptor with UTP, a relatively selective agonist of the P2Y2R, increases neurite outgrowth. Consistent with the accepted role of cofilin in the regulation of neurite extension, results indicate that incubation of IL-1β-treated mPCNs with UTP increases the phosphorylation of cofilin, a response absent in PCNs isolated from P2Y2R(-/-) mice. Other findings indicate that function-blocking anti-αv β3/5 integrin antibodies prevent UTP-induced cofilin activation in IL-1β-treated mPCNs, suggesting that established P2Y2R/αv β3/5 interactions that promote G12 -dependent Rho activation lead to cofilin phosphorylation involved in neurite extension. Cofilin phosphorylation induced by UTP in IL-1β-treated mPCNs is also decreased by inhibitors of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), suggesting a role for P2Y2R-mediated and Gq-dependent calcium mobilization in neurite outgrowth. Taken together, these studies indicate that up-regulation of P2Y2Rs in mPCNs under pro-inflammatory conditions can promote cofilin-dependent neurite outgrowth, a neuroprotective response that may be a novel pharmacological target in the treatment of neurodegenerative diseases.

Functional impairment of microglia coincides with Beta-amyloid deposition in mice with Alzheimer-like pathology

Microglial cells closely interact with senile plaques in Alzheimer’s disease and acquire the morphological appearance of an activated phenotype. The significance of this microglial phenotype and the impact of microglia for disease progression have remained controversial. To uncover and characterize putative changes in the functionality of microglia during Alzheimer’s disease, we directly assessed microglial behavior in two mouse models of Alzheimer’s disease. Using in vivo two-photon microscopy and acute brain slice preparations, we found that important microglial functions - directed process motility and phagocytic activity - were strongly impaired in mice with Alzheimer’s disease-like pathology compared to age-matched non-transgenic animals. Notably, impairment of microglial function temporally and spatially correlated with Aβ plaque deposition, and phagocytic capacity of microglia could be restored by interventionally decreasing amyloid burden by Aβ vaccination. These data suggest that major microglial functions progressively decline in Alzheimer’s disease with the appearance of Aβ plaques, and that this functional impairment is reversible by lowering Aβ burden, e.g. by means of Aβ vaccination.

Peripheral inflammation in neurodegeneration

Neuroinflammation is now a well-characterised feature of neurodegenerative diseases. Immune dysfunction outside the central nervous system is also increasingly recognised as part of the diseases. Peripheral inflammation has emerged as a modulator of disease progression and neuropathology in several neurodegenerative diseases, making it targetable in new therapeutic approaches. In addition, the easy accessibility of blood immune cells and markers makes them ideal candidates for use as possible biomarkers and a potential model of central immune cells.

Neuroinflammation and neuronal loss precede Aβ plaque deposition in the hAPP-J20 mouse model of Alzheimer's disease

Recent human trials of treatments for Alzheimer's disease (AD) have been largely unsuccessful, raising the idea that treatment may need to be started earlier in the disease, well before cognitive symptoms appear. An early marker of AD pathology is therefore needed and it is debated as to whether amyloid-βAβ? plaque load may serve this purpose. We investigated this in the hAPP-J20 AD mouse model by studying disease pathology at 6, 12, 24 and 36 weeks. Using robust stereological methods, we found there is no neuron loss in the hippocampal CA3 region at any age. However loss of neurons from the hippocampal CA1 region begins as early as 12 weeks of age. The extent of neuron loss increases with age, correlating with the number of activated microglia. Gliosis was also present, but plateaued during aging. Increased hyperactivity and spatial memory deficits occurred at 16 and 24 weeks. Meanwhile, the appearance of plaques and oligomeric Aβ were essentially the last pathological changes, with significant changes only observed at 36 weeks of age. This is surprising given that the hAPP-J20 AD mouse model is engineered to over-expresses Aβ. Our data raises the possibility that plaque load may not be the best marker for early AD and suggests that activated microglia could be a valuable marker to track disease progression.