Increased IL-1beta in cortex of aged rats is accompanied by downregulation of ERK and PI-3 kinase

High-fat diet and aging-associated memory impairments persist in the absence of microglia in female rats

Aging is associated with a priming of microglia such that they are hypersensitive to further immune challenges. As such high-fat diet during aging can have detrimental effects on cognition that is not seen in the young. However, conflicting findings also suggest that obesity may protect against cognitive decline during aging. Given this uncertainty we aimed here to examine the role of microglia in high-fat, high-sucrose diet (HFSD)-induced changes in cognitive performance in the aging brain. We hypothesised that 8 weeks of HFSD-feeding would alter microglia and the inflammatory milieu in aging and worsen aging-related cognitive deficits in a microglia-dependent manner. We found that both aging and HFSD reduced hippocampal neuron numbers and open field exploration; they also impaired recognition memory. However, the aging-related deficits occurred in the absence of a pro-inflammatory response and the deficits in memory performance persisted after depletion of microglia in the Cx3cr1-Dtr knock-in rat. Our data suggest that mechanisms additional to the acute microglial contribution play a role in aging- and HFSD-associated memory dysfunction.

Aberrant Cerebral Iron Trafficking Co-morbid With Chronic Inflammation: Molecular Mechanisms and Pharmacologic Intervention

The redox properties that make iron an essential nutrient also make iron an efficient pro-oxidant. Given this nascent cytotoxicity, iron homeostasis relies on a combination of iron transporters, chaperones, and redox buffers to manage the non-physiologic aqueous chemistry of this first-row transition metal. Although a mechanistic understanding of the link between brain iron accumulation (BIA) and neurodegenerative diseases is lacking, BIA is co-morbid with the majority of cognitive and motor function disorders. The most prevalent neurodegenerative disorders, including Alzheimer's Disease (AD), Parkinson's Disease (PD), Multiple System Atrophy (MSA), and Multiple Sclerosis (MS), often present with increased deposition of iron into the brain. In addition, ataxias that are linked to mutations in mitochondrial-localized proteins (Friedreich's Ataxia, Spinocerebellar Ataxias) result in mitochondrial iron accumulation and degradation of proton-coupled ATP production leading to neuronal degeneration. A comorbidity common in the elderly is a chronic systemic inflammation mediated by primary cytokines released by macrophages, and acute phase proteins (APPs) released subsequently from the liver. Abluminal inflammation in the brain is found downstream as a result of activation of astrocytes and microglia. Reasonably, the iron that accumulates in the brain comes from the cerebral vasculature via the microvascular capillary endothelial cells whose tight junctions represent the blood-brain barrier. A premise amenable to experimental interrogation is that inflammatory stress alters both the trans- and para-cellular flux of iron at this barrier resulting in a net accumulation of abluminal iron over time. This review will summarize the evidence that lends support to this premise; indicate the mechanisms that merit delineation; and highlight possible therapeutic interventions based on this model.

Normal aging, motor neurone disease, and Alzheimer's disease are characterized by cortical changes in inflammatory cytokines

The role of increased brain inflammation in the development of neurodegenerative diseases is unclear. Here, we have compared cytokine changes in normal aging, motor neurone disease (MND), and Alzheimer's disease (AD). After an initial analysis, six candidate cytokines, interleukin (IL)- 4, 5, 6, 10, macrophage inhibitory protein (MIP)-1α, and fibroblast growth factor (FGF)-2, showing greatest changes were assayed in postmortem frozen human superior frontal gyri (n = 12) of AD patients, aging and young adult controls along with the precentral gyrus (n = 12) of MND patients. Healthy aging was associated with decreased anti-inflammatory IL-10 and FGF-2 levels. AD prefrontal cortex was associated with increased levels of IL-4, IL-5, and FGF-2, with the largest increase seen for FGF-2. Notwithstanding differences in the specific frontal lobe gyrus sampled, MND patients' primary motor cortex (precentral gyrus) was associated with increased levels of IL-5, IL-6, IL-10, and FGF-2 compared to the aging prefrontal cortex (superior frontal gyrus). Immunocytochemistry showed that FGF-2 is expressed in neurons, astrocytes, and microglia in normal aging prefrontal cortex, AD prefrontal cortex, and MND motor cortex. We report that healthy aging and age-related neurodegenerative diseases have different cortical inflammatory signatures that are characterized by increased levels of anti-inflammatory cytokines and call into question the view that increased inflammation underlies the development of age-related neurodegenerative diseases.

The killifish visual system as an in vivo model to study brain aging and rejuvenation

Worldwide, people are getting older, and this prolonged lifespan unfortunately also results in an increased prevalence of age-related neurodegenerative diseases, contributing to a diminished life quality of elderly. Age-associated neuropathies typically include diseases leading to dementia (Alzheimer's and Parkinson's disease), as well as eye diseases such as glaucoma and age-related macular degeneration. Despite many research attempts aiming to unravel aging processes and their involvement in neurodegeneration and functional decline, achieving healthy brain aging remains a challenge. The African turquoise killifish (Nothobranchius furzeri) is the shortest-lived reported vertebrate that can be bred in captivity and displays many of the aging hallmarks that have been described for human aging, which makes it a very promising biogerontology model. As vision decline is an important hallmark of aging as well as a manifestation of many neurodegenerative diseases, we performed a comprehensive characterization of this fish's aging visual system. Our work reveals several aging hallmarks in the killifish retina and brain that eventually result in a diminished visual performance. Moreover, we found evidence for the occurrence of neurodegenerative events in the old killifish retina. Altogether, we introduce the visual system of the fast-aging killifish as a valuable model to understand the cellular and molecular mechanisms underlying aging in the vertebrate central nervous system. These findings put forward the killifish for target validation as well as drug discovery for rejuvenating or neuroprotective therapies ensuring healthy aging.

Neuroinflammation in Alzheimer's disease and beneficial action of luteolin

Alzheimer's disease (AD), already the world's most common form of dementia, is projected to continue increasing in prevalence over the next several decades. The current lack of understanding of the pathogenesis of AD has hampered the development of effective treatments. Historically, AD research has been predicated on the amyloid cascade hypothesis (ACH), which attributes disease progression to the build-up of amyloid protein. However, multiple clinical studies of drugs interfering with ACH have failed to show any benefit demonstrating that AD etiology is more complex than previously thought. Here we review the current literature on the emerging key role of neuroinflammation, especially activation of microglia, in AD pathogenesis. Moreover, we provide compelling evidence that certain flavonoids, especially luteolin formulated in olive pomace oil together with hydroxytyrosol, offers a reasonable prophylactic treatment approach due to its many beneficial actions.

Chronic noncancer pain is not associated with accelerated brain aging as assessed by structural magnetic resonance imaging in patients treated in specialized outpatient clinics

Chronic pain is often associated with changes in brain structure and function, and also cognitive deficits. It has been noted that these chronic pain-related alterations may resemble changes found in healthy aging, and thus may represent accelerated or premature aging of the brain. Here, we test the hypothesis that patients with chronic noncancer pain demonstrate accelerated brain aging compared with healthy control subjects. The predicted brain age of 59 patients with chronic pain (mean chronological age ± SD: 53.0 ± 9.0 years; 43 women) and 60 pain-free healthy controls (52.6 ± 9.0 years; 44 women) was determined using the software brainageR. This software segments the individual T1-weighted structural MR images into gray and white matter and compares gray and white matter images with a large (n = 2001) training set of structural images, using machine learning. Finally, brain age delta, which is the predicted brain age minus chronological age, was calculated and compared across groups. This study provided no evidence for the hypothesis that chronic pain is associated with accelerated brain aging (Welch t test, P = 0.74, Cohen's d = 0.061). A Bayesian independent-samples t test indicated moderate evidence in favor of the null hypothesis (BF01 = 4.875, ie, group means were equal). Our results provide indirect support for recent models of pain-related changes of brain structure, brain function, and cognitive functions. These models postulate network-specific maladaptive plasticity, rather than widespread or global neural degeneration.

Dietary fish hydrolysate supplementation containing n-3 LC-PUFAs and peptides prevents short-term memory and stress response deficits in aged mice

Brain aging is characterized by a decline in cognitive functions, which can lead to the development of neurodegenerative pathologies. Age-related spatial learning and memory deficits are associated with a chronic low-grade inflammation. Anxiety disorders and stress response alterations, occurring for a part of the elderly, have also been linked to an increased neuroinflammation and thus, an accelerated cognitive decline. Nutrition is an innovative strategy to prevent age-related cognitive impairments. Among the nutrients, n-3 long chain polyunsaturated fatty acids (LC-PUFAs) and low molecular weight peptides from proteins, especially those from marine resources, are good candidates for their immunomodulatory, anxiolytic and neuroprotective properties. The aim of this study is to determine the combined effect of n-3 LC-PUFAs and low molecular weight peptides on cognitive functions, and their mechanism of action. We are the first to show that a dietary supplementation with a fish hydrolysate containing n-3 LC-PUFAs and low molecular weight peptides prevented the age-related spatial short-term memory deficits and modulated navigation strategies adopted during spatial learning. In addition, the fish hydrolysate displayed anxiolytic activities with the reduction of anxiety-like behaviour in aged mice, restored the plasmatic corticosterone levels similar to adult animals following an acute stress and modulated the hypothalamic stress response. These effects on behaviour can be explained by the immunomodulatory and neuroprotective properties of the fish hydrolysate that limited microgliosis in vivo, decreased LPS-induced expression of pro-inflammatory cytokines and increased the expression of growth factors such as BDNF and NGF in vitro. Thus, n-3 LC-PUFAs and low molecular weight peptides contained in the fish hydrolysate can play an important role in the limitation of neuroinflammation and stress response alterations during aging and represent a potential strategy for the prevention of age-related cognitive decline.

An Overview of Crucial Dietary Substances and Their Modes of Action for Prevention of Neurodegenerative Diseases

Neurodegenerative diseases, namely Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis, Huntington's disease, and multiple sclerosis are becoming one of the main health concerns due to the increasing aging of the world's population. These diseases often share the same biological mechanisms, including neuroinflammation, oxidative stress, and/or protein fibrillation. Recently, there have been many studies published pointing out the possibilities to reduce and postpone the clinical manifestation of these deadly diseases through lifelong consumption of some crucial dietary substances, among which phytochemicals (e.g., polyphenols) and endogenous substances (e.g., acetyl-L-carnitine, coenzyme Q10, n-3 poysaturated fatty acids) showed the most promising results. Another important issue that has been pointed out recently is the availability of these substances to the central nervous system, where they have to be present in high enough concentrations in order to exhibit their neuroprotective properties. As so, such the aim of this review is to summarize the recent findings regarding neuroprotective substances, their mechanisms of action, as well as to point out therapeutic considerations, including their bioavailability and safety for humans.

Progranulin suppresses the age-dependent enhancement of neuronal activity in the hypothalamus

Our previous investigations revealed that progranulin (PGRN) is a lysosomal protein involved in hippocampal neurogenesis and neuroinflammation. However, the possible involvement of PGRN in regulating inflammatory response and mediating neuronal activity is still not well-defined. Here, we demonstrate that PGRN deficiency enhances the age-dependent increase of neuronal activity in the paraventricular nucleus (PVN) of the hypothalamus. Aging increased neuronal activity in the PVN of the hypothalamus, and PGRN deficiency enhanced the effects of age on hypothalamic neuronal activity. Aging increased the lysosomal biogenesis and inflammatory response in microglia, which was also aggravated in PGRN-knockout mice. Moreover, PGRN deficiency enhanced interleukin-1 beta and lysosomal genes levels. These results suggest that PGRN deficiency may enhance the age-dependent increase of neuronal activity possibly because PGRN facilitates immunological responses through regulating lysosomal function.

Cannabidiol Counteracts the Psychotropic Side-Effects of Δ-9-Tetrahydrocannabinol in the Ventral Hippocampus through Bidirectional Control of ERK1-2 Phosphorylation

Evidence suggests that the phytocannabinoids Δ-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) differentially regulate salience attribution and psychiatric risk. The ventral hippocampus (vHipp) relays emotional salience via control of dopamine (DA) neuronal activity states, which are dysregulated in psychosis and schizophrenia. Using in vivo electrophysiology in male Sprague Dawley rats, we demonstrate that intra-vHipp THC strongly increases ventral tegmental area (VTA) DA neuronal frequency and bursting rates, decreases GABA frequency, and amplifies VTA beta, gamma and ε oscillatory magnitudes via modulation of local extracellular signal-regulated kinase phosphorylation (pERK1-2). Remarkably, whereas intra-vHipp THC also potentiates salience attribution in morphine place-preference and fear conditioning assays, CBD coadministration reverses these changes by downregulating pERK1-2 signaling, as pharmacological reactivation of pERK1-2 blocked the inhibitory properties of CBD. These results identify vHipp pERK1-2 signaling as a critical neural nexus point mediating THC-induced affective disturbances and suggest a potential mechanism by which CBD may counteract the psychotomimetic and psychotropic side effects of THC.SIGNIFICANCE STATEMENT Strains of marijuana with high levels of delta-9-tetrahydrocannabinol (THC) and low levels of cannabidiol (CBD) have been shown to underlie neuropsychiatric risks associated with high-potency cannabis use. However, the mechanisms by which CBD mitigates the side effects of THC have not been identified. We demonstrate that THC induces cognitive and affective abnormalities resembling neuropsychiatric symptoms directly in the hippocampus, while dysregulating dopamine activity states and amplifying oscillatory frequencies in the ventral tegmental area via modulation of the extracellular signal-regulated kinase (ERK) signaling pathway. In contrast, CBD coadministration blocked THC-induced ERK phosphorylation, and prevented THC-induced behavioral and neural abnormalities. These findings identify a novel molecular mechanism that may account for how CBD functionally mitigates the neuropsychiatric side effects of THC.

Can krill oil be of use for counteracting neuroinflammatory processes induced by high fat diet and aging?

Most neurodegenerative diseases, such as Alzheimer's and Parkinson's disease, demonstrate preceding or on-going inflammatory processes. Therefore, discovering effective means of counteracting detrimental inflammatory mediators in the brain could help alter aging-related disease onset and progression. Fish oil and marine-derived omega-3, long-chain polyunsaturated fatty acids (LC n-3) have shown promising anti-inflammatory effects both systemically and centrally. More specifically, krill oil (KO), extracted from small Antarctic crustaceans, is an alternative type of LC n-3 with reported health benefits including improvement of spatial memory and learning, memory loss, systemic inflammation and depression symptoms. Similar to the more widely studied fish oil, KO contains the long chain fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) which are essential for basic brain functions. Moreover, the phospholipid bound nature of fatty acids found in KO improves bioavailability and efficiency of absorption, thus supporting the belief that KO may offer a superior method of dietary n-3 delivery. Finally, KO contains astaxanthin, an antioxidant capable of reducing potentially excessive oxidative stress and inflammation within the brain. This review will discuss the potential benefits of KO over other marine-based LC n-3 on brain inflammation and cognitive function in the context of high fat diets and aging.

Astrocyte activation and altered metabolism in normal aging, age-related CNS diseases, and HAND

Astrocytes regulate local cerebral blood flow, maintain ion and neurotransmitter homeostasis, provide metabolic support, regulate synaptic activity, and respond to brain injury, insults, and infection. Because of their abundance, extensive connectivity, and multiple roles in the brain, astrocytes are intimately involved in normal functioning of the CNS and their dysregulation can lead to neuronal dysfunction. In normal aging, decreased biological functioning and reduced cognitive abilities are commonly experienced in individuals free of overt neurological disease. Moreover, in several age-related CNS diseases, chronic inflammation and altered metabolism have been reported. Since people with HIV (PWH) are reported to experience rapid aging with chronic inflammation, altered brain metabolism is likely to be exacerbated. In fact, many studies report altered metabolism in astrocytes in diseases such as Alzheimer's, Parkinson's, and HIV. This review will address the roles of astrocyte activation and altered metabolism in normal aging, in age-related CNS disease, and in HIV-associated neurocognitive disorders.

Distinguishing normal brain aging from the development of Alzheimer's disease: inflammation, insulin signaling and cognition

As populations age, prevalence of Alzheimer's disease (AD) is rising. Over 100 years of research has provided valuable insights into the pathophysiology of the disease, for which age is the principal risk factor. However, in recent years, a multitude of clinical trial failures has led to pharmaceutical corporations becoming more and more unwilling to support drug development in AD. It is possible that dependence on the amyloid cascade hypothesis as a guide for preclinical research and drug discovery is part of the problem. Accumulating evidence suggests that amyloid plaques and tau tangles are evident in non-demented individuals and that reducing or clearing these lesions does not always result in clinical improvement. Normal aging is associated with pathologies and cognitive decline that are similar to those observed in AD, making differentiation of AD-related cognitive decline and neuropathology challenging. In this mini-review, we discuss the difficulties with discerning normal, age-related cognitive decline with that related to AD. We also discuss some neuropathological features of AD and aging, including amyloid and tau pathology, synapse loss, inflammation and insulin signaling in the brain, with a view to highlighting cognitive or neuropathological markers that distinguish AD from normal aging. It is hoped that this review will help to bolster future preclinical research and support the development of clinical tools and therapeutics for AD.

The Role of Physical Exercise and Omega-3 Fatty Acids in Depressive Illness in the Elderly

Background:

In adulthood, depression is the most common type of mental illness and will be the second leading cause of disease by 2020. Major depression dramatically affects the function of the central nervous system and degrades the quality of life, especially in old age.

Several mechanisms underlie the pathophysiology of depressive illness, since it has a multifactorial etiology. Human and an-imal studies have demonstrated that depression is mainly associated with imbalances in neurotransmitters and neurotrophins, hypothalamic-pituitary-adrenal axis alterations, brain volume changes, neurogenesis dysfunction, and dysregulation of in-flammatory pathways. Also the gut microbiota may influence mental health outcomes.

Although depression is not a consequence of normal aging, depressive disorders are common in later life, even if often undi-agnosed or mis-diagnosed in old age. When untreated, depression reduces life expectancy, worsens medical illnesses, en-hances health care costs and is the primary cause of suicide among older people. To date, the underpinnings of depression in the elderly are still to be understood, and the pharmacological treatment is the most commonly used therapy.

Objective:

Since a sedentary lifestyle and poor eating habits have recently emerged as crucial contributors to the genesis and course of depression, in the present review, we have focused on the effects of physical activity and omega-3 fatty acids on depressive illness in the elderly.

Results:

A growing literature indicates that both exercise and dietary interventions can promote mental health throughout one’s lifespan.

Conclusion:

There thus emerges the awareness that an active lifestyle and a balanced diet may constitute valid low-cost pre-vention strategies to counteract depressive illness in the elderly.

Dexamethasone Induces a Specific Form of Ramified Dysfunctional Microglia

The functional status of dynamic microglial cells plays an important role in maintaining homeostasis of microenvironment in CNS. In a previous study, we reported that microglia phenotype might be involved in stress vulnerability and depression recurrence. Here, we aimed to clarify a character of microglia exposed persistently to glucocorticoid (GC), which is representative a stress hormone, in primary cultured microglial cells. Five nanomolars of dexamethasone (DEX, GC agonist) for 72 h decreased CX3CR1 and CD200R expression and induced ramified form of microglial cells in similar morphology to in vivo resident microglia. However, the ramified form of microglia did not increase microglia signature genes such as P2RY12, OLFML3, TMEM119, and TGFBR1. In addition, DEX-treated microglia showed a reduction of phagocytosis function, pro-and anti-inflammatory cytokine production, and cell proliferation. DEX washout did not restore these changes. Based on transcriptomic analysis and functional characters of DEX-treated microglia, we performed senescence-associated beta-galactosidase (SA-β gal) assay in DEX-treated microglia and DEX-treated microglia showed more SA-β gal activity with alteration of cell cycle-related genes. Thus, our results suggest that DEX can induce a specific phenotype of microglia (like-senescence).

Inflammation, insulin signaling and cognitive function in aged APP/PS1 mice

Cognitive dysfunction and neuroinflammation are typical in Alzheimer's disease (AD), but are also associated with normal aging, albeit less severely. Insulin resistance in the brain has been demonstrated in AD patients and is thought to be involved in AD pathophysiology. Using 15-18 month-old APP/PS1 mice, this study measured peripheral and central insulin signaling and sensitivity, inflammatory markers in brain and plasma and oxidative stress and synapse density in the brain. Novel object recognition, Morris water maze and reversal water maze tasks were performed to assess cognitive function in aged APP/PS1 mice and wild type littermates. Glucose tolerance and insulin sensitivity were similar in APP/PS1 mice and wild type controls, however IRS-1 pSer⁶¹⁶ was increased in cortex and dentate gyrus of APP/PS1 mice. Recognition and spatial memory was impaired in both APP/PS1 and wild type mice, however learning impairments were apparent in APP/PS1 mice. Expression of GLP-1 receptor, ERK2, IKKβ, mTOR, PKCθ, NF-κB1 and TLR4 was similar between aged APP/PS1 mice and age-matched wild types. Compared to age-matched wild type mice, IFNγ and IL-4 were increased in brains of APP/PS1 mice. These results suggest that normal aging may be associated with enhanced neuroinflammation, oxidative stress, and cognitive decline, however distinctions are apparent in the brain of APP/PS1 mice in terms of inflammation and insulin signaling and in certain cognitive domains. Demarcation of pathological events that distinguish AD from normal aging will allow for improvements in diagnostic tools and the development of more effective therapeutics.

Lifelong environmental enrichment in the absence of exercise protects the brain from age-related cognitive decline

Environmental manipulations enhance neuroplasticity, with enrichment-induced cognitive improvements linked to increased expression of growth factors and enhanced hippocampal neurogenesis. Environmental enrichment (EE) is defined as the addition of social, physical and somatosensory stimulation into an animal's environment via larger group housing, extra objects and, often, running wheels. Previous studies from our laboratory report that physical activity is a potent memory enhancer but that long-term environmental stimulation can be as effective as exercise at ameliorating age-related memory decline. To assess the effects of EE, in the absence of exercise, rats were housed in continuous enriched conditions for 20 months and memory assessed at young, middle aged and aged timepoints. MRI scans were also performed at these timepoints to assess regional changes in grey matter and blood flow with age, and effects of EE upon these measures. Results show an age-related decline in recognition, spatial and working memory that was prevented by EE. A parallel reduction in βNGF in hippocampus, and cell proliferation in the dentate gyrus, was prevented by EE. Furthermore, EE attenuated an age-related increase in apoptosis and expression of pro-inflammatory markers IL-1β and CD68. Long-term EE induced region-specific changes in grey matter intensity and partially rescued age-related reductions in cerebral blood flow. This study demonstrates that sensory enrichment alone can ameliorate many features typical of the ageing brain, such as increases in apoptosis and pro-inflammatory markers. Furthermore, we provide novel data on enrichment-induced regional grey matter alterations and age-related changes in blood flow in the rat. This article is part of the Special Issue entitled "Neurobiology of Environmental Enrichment".

Alzheimer's Disease: The Role of Microglia in Brain Homeostasis and Proteopathy

Brain aging is central to late-onset Alzheimer's disease (LOAD), although the mechanisms by which it occurs at protein or cellular levels are not fully understood. Alzheimer's disease is the most common proteopathy and is characterized by two unique pathologies: senile plaques and neurofibrillary tangles, the former accumulating earlier than the latter. Aging alters the proteostasis of amyloid-β peptides and microtubule-associated protein tau, which are regulated in both autonomous and non-autonomous manners. Microglia, the resident phagocytes of the central nervous system, play a major role in the non-autonomous clearance of protein aggregates. Their function is significantly altered by aging and neurodegeneration. This is genetically supported by the association of microglia-specific genes, TREM2 and CD33, and late onset Alzheimer's disease. Here, we propose that the functional characterization of microglia, and their contribution to proteopathy, will lead to a new therapeutic direction in Alzheimer's disease research.

Brainstem cytokine changes in healthy ageing and Motor Neurone Disease

Neuroinflammation is linked to healthy ageing, but its role in the development of age-related neurodegenerative diseases is unclear. In this pilot study we used a multiplex assay approach to compare 27 cytokines in 6 young adult and 6 ageing control brainstems with those in 6 MND brainstems. We report that healthy ageing is associated with significantly increased brainstem levels of IL-1β, IP-10 and MIP-1β which co-localise immunocytochemically to astrocytes. MND brainstem is also characterised by a general increase in both pro- and anti-cytokine levels, but fails to show the expected age-related increase in MIP-1β and IP-10. This pilot study is the first to show that MND is associated with a failure of specific features of the normal age-related neuroinflammatory process. We suggest that our pilot data indicates that neuroinflammation during healthy ageing may not always be detrimental to motoneuronal survival and that age-related neurodegenerative diseases, such as MND, may instead result from defective neuroinflammation.

The brain, sirtuins, and ageing

In mammals, recent studies have demonstrated that the brain, the hypothalamus in particular, is a key bidirectional integrator of humoral and neural information from peripheral tissues, thus influencing ageing both in the brain and at the 'systemic' level. CNS decline drives the progressive impairment of cognitive, social and physical abilities, and the mechanisms underlying CNS regulation of the ageing process, such as microglia-neuron networks and the activities of sirtuins, a class of NAD⁺-dependent deacylases, are beginning to be understood. Such mechanisms are potential targets for the prevention or treatment of age-associated dysfunction and for the extension of a healthy lifespan.

Mild Inflammatory Profile without Gliosis in the c-Rel Deficient Mouse Modeling a Late-Onset Parkinsonism

The impact of neuroinflammation and microglial activation to Parkinson's disease (PD) progression is still debated. Post-mortem analysis of PD brains has shown that neuroinflammation and microgliosis are key features of end-stage disease. However, microglia neuroimaging studies and evaluation of cerebrospinal fluid (CSF) cytokines in PD patients at earlier stages do not support the occurrence of a pronounced neuroinflammatory process. PD animal models recapitulating the motor and non-motor features of the disease, and the slow and progressive neuropathology, can be of great advantage in understanding whether and how neuroinflammation associates with the onset of symptoms and neuronal loss. We recently described that 18-month-old NF-κB/c-Rel deficient mice (c-rel^-/-) develop a spontaneous late-onset PD-like phenotype encompassing L-DOPA-responsive motor impairment, nigrostriatal neuron degeneration, α-synuclein and iron accumulation. To assess whether inflammation and microglial activation accompany the onset and the progression of PD-like pathology, we investigated the expression of cytokines (interleukin 1 beta (Il1b), interleukin 6 (Il6)) and microglial/macrophage activation markers (Fc gamma receptor III (Fcgr3), mannose receptor 1 (Mrc1), chitinase-like 3 (Ym1), arginase 1 (Arg 1), triggering receptor expressed on myeloid cells 2 (Trem2)), together with microglial ionized calcium binding adapter molecule 1 (Iba1) and astrocyte glial fibrillary acidic protein (GFAP) immunolabeling, in the substantia nigra (SN) of c-rel^-/- mice, at premotor (4- and 13-month-old) and motor phases (18-month-old). By quantitative real-time RT-PCR we found increased M2c microglial/macrophage markers expression (Mrc1 and Arg1) in 4-month-old c-rel^-/- mice. M2-type transcription dropped down in 13-month-old c-rel^-/- mice. At this age, the pro-inflammatory Il1b, but not Il6 or the microglia-macrophage M1-polarization marker Fcgr3/CD16, increased when compared to wild-type (wt). Furthermore, no significant variation in the transcription of inflammatory and microglial/macrophage activation genes was present in 18-month-old c-rel^-/- mice, that display motor dysfunctions and dopaminergic neuronal loss. Immunofluorescence analysis of Iba1-positive cells in the SN revealed no sign of overt microglial activation in c-rel^-/- mice at all the time-points. MRC1-Iba1-positive cells were identified as non-parenchymal macrophages in 4-month-old c-rel^-/- mice. Finally, no sign of astrogliosis was detected in the SN of the diverse animal groups. In conclusion, this study supports the presence of a mild inflammatory profile without evident signs of gliosis in c-rel^-/- mice up to 18 months of age. It suggests that symptomatic PD-like phenotype can develop in the absence of concomitant severe inflammatory process.

Microglia Priming with Aging and Stress

The population of aged individuals is increasing worldwide and this has significant health and socio-economic implications. Clinical and experimental studies on aging have discovered myriad changes in the brain, including reduced neurogenesis, increased synaptic aberrations, higher metabolic stress, and augmented inflammation. In rodent models of aging, these alterations are associated with cognitive decline, neurobehavioral deficits, and increased reactivity to immune challenges. In rodents, caloric restriction and young blood-induced revitalization reverses the behavioral effects of aging. The increased inflammation in the aged brain is attributed, in part, to the resident population of microglia. For example, microglia of the aged brain are marked by dystrophic morphology, elevated expression of inflammatory markers, and diminished expression of neuroprotective factors. Importantly, the heightened inflammatory profile of microglia in aging is associated with a 'sensitized' or 'primed' phenotype. Mounting evidence points to a causal link between the primed profile of the aged brain and vulnerability to secondary insults, including infections and psychological stress. Conversely, psychological stress may also induce aging-like sensitization of microglia and increase reactivity to secondary challenges. This review delves into the characteristics of neuroinflammatory signaling and microglial sensitization in aging, its implications in psychological stress, and interventions that reverse aging-associated deficits.

Functional and Structural Benefits Induced by Omega-3 Polyunsaturated Fatty Acids During Aging

BACKGROUND

Omega-3 polyunsaturated fatty acids (n-3 PUFA) are structural components of the brain and are indispensable for neuronal membrane synthesis. Along with decline in cognition, decreased synaptic density and neuronal loss, normal aging is accompanied by a reduction in n-3 PUFA concentration in the brain in both humans and rodents. Recently, many clinical and experimental studies have demonstrated the importance of n-3 PUFA in counteracting neurodegeneration and agerelated dysfunctions.

METHODS

This review will focus on the neuroprotective effects of n-3 PUFA on cognitive impairment, neuroinflammation and neurodegeneration during normal aging. Multiple pathways of n-3 PUFA preventive action will be examined.

RESULTS

Namely, n-3 PUFA have been shown to increase the levels of several signaling factors involved in synaptic plasticity, thus leading to the increase of dendritic spines and synapses as well as the enhancement of hippocampal neurogenesis even at old age. In elderly subjects n-3 PUFA exert anti-inflammatory effects associated with improved cognitive functions. Interestingly, growing evidence highlights n-3 PUFA efficacy in preventing the loss of both gray and white matter volume and integrity.

CONCLUSION

This review shows that n-3 PUFA are essential for a successful aging and appear as ideal cognitive enhancers to be implemented in nutritional interventions for the promotion of healthy aging.

Effects of Omega-3 Fatty Acid Supplementation on Cognitive Functions and Neural Substrates: A Voxel-Based Morphometry Study in Aged Mice

Human and experimental studies have revealed putative neuroprotective and pro-cognitive effects of omega-3 polyunsaturated fatty acids (n-3 PUFA) in aging, evidencing positive correlations between peripheral n-3 PUFA levels and regional grey matter (GM) volume, as well as negative correlations between dietary n-3 PUFA levels and cognitive deficits. We recently showed that n-3 PUFA supplemented aged mice exhibit better hippocampal-dependent mnesic functions, along with enhanced cellular plasticity and reduced neurodegeneration, thus supporting a role of n-3 PUFA supplementation in preventing cognitive decline during aging. To corroborate these initial results and develop new evidence on the effects of n-3 PUFA supplementation on brain substrates at macro-scale level, here we expanded behavioral analyses to the emotional domain (anxiety and coping skills), and carried out a fine-grained regional GM volumetric mapping by using high-resolution MRI-based voxel-based morphometry. The behavioral effects of 8 week n-3 PUFA supplementation were measured on cognitive (discriminative, spatial and social) and emotional (anxiety and coping) abilities of aged (19 month-old at the onset of study) C57B6/J mice. n-3 PUFA supplemented mice showed better mnesic performances as well as increased active coping skills. Importantly, these effects were associated with enlarged regional hippocampal, retrosplenial and prefrontal GM volumes, and with increased post mortem n-3 PUFA brain levels. These findings indicate that increased dietary n-3 PUFA intake in normal aging can improve fronto-hippocampal GM structure and function, an effect present also when the supplementation starts at late age. Our data are consistent with a protective role of n-3 PUFA supplementation in counteracting cognitive decline, emotional dysfunctions and brain atrophy.

Age decreases macrophage IL-10 expression: Implications for functional recovery and tissue repair in spinal cord injury

Macrophages with different activation states are present after spinal cord injury (SCI). M1 macrophages purportedly promote secondary injury processes while M2 cells support axon growth. The average age at the time of SCI has increased in recent decades, however, little is known about how different physiological factors contribute to macrophage activation states after SCI. Here we investigate the effect of age on IL-10, a key indicator of M2 macrophage activation. Following mild-moderate SCI in 4 and 14 month old (MO) mice we detected significantly reduced IL-10 expression with age in the injured spinal cord. Specifically, CD86/IL-10 positive macrophages, also known as M2b or regulatory macrophages, were reduced in 14 vs. 4 MO SCI animals. This age-dependent shift in macrophage phenotype was associated with impaired functional recovery and enhanced tissue damage in 14-month-old SCI mice. In vitro, M2b macrophages release anti-inflammatory cytokines without causing neurotoxicity, suggesting that imbalances in the M2b response in 14-month-old mice may be contributing to secondary injury processes. Our data indicate that age is an important factor that regulates SCI inflammation and recovery even to mild-moderate injury. Further, alterations in macrophage activation states may contribute to recovery and we have identified the M2b phenotype as a potential target for therapeutic intervention.

N-3 polyunsaturated fatty acids in animal models with neuroinflammation: An update

Neuroinflammation is a characteristic of a multitude of neurological and psychiatric disorders. Modulating inflammatory pathways offers a potential therapeutic target in these disorders. Omega-3 polyunsaturated fatty acids have anti-inflammatory and pro-resolving properties in the periphery, however, their effect on neuroinflammation is less studied. This review summarizes 61 animal studies that tested the effect of omega-3 polyunsaturated fatty acids on neuroinflammatory outcomes in vivo in various models including stroke, spinal cord injury, aging, Alzheimer's disease, Parkinson's disease, lipopolysaccharide and IL-1β injections, diabetes, neuropathic pain, traumatic brain injury, depression, surgically induced cognitive decline, whole body irradiation, amyotrophic lateral sclerosis, N-methyl-D-aspartate-induced excitotoxicity and lupus. The evidence presented in this review suggests anti-neuroinflammatory properties of omega-3 polyunsaturated fatty acids, however, it is not clear by which mechanism omega-3 polyunsaturated fatty acids exert their effect. Future research should aim to isolate the effect of omega-3 polyunsaturated fatty acids on neuroinflammatory signaling in vivo and elucidate the mechanisms underlying these effects.

Coccomyxa Gloeobotrydiformis Improves Learning and Memory in Intrinsic Aging Rats

Declining in learning and memory is one of the most common and prominent problems during the aging process. Neurotransmitter changes, oxidative stress, mitochondrial dysfunction and abnormal signal transduction were considered to participate in this process. In the present study, we examined the effects of Coccomyxa gloeobotrydiformis (CGD) on learning and memory ability of intrinsic aging rats. As a result, CGD treated (50 mg/kg·d or 100 mg/kg ·d for a duration of 8 weeks) 22-month-old male rats, which have shown significant improvement on learning and spatial memory ability compared with control, which was evidently revealed in both the hidden platform tasks and probe trials. The following immunohistochemistry and Western blot experiments suggested that CGD could increase the content of Ach and thereby improve the function of the cholinergic neurons in the hippocampus, and therefore also improving learning and memory ability of the aged rats by acting as an anti-inflammatory agent. The effects of CGD on learning and memory might also have an association with the ERK/CREB signalling. The results above suggest that the naturally made drug CGD may have several great benefit as a multi-target drug in the process of prevention and/or treatment of age-dependent cognitive decline and aging process.

Long-chain omega-3 fatty acids and the brain: a review of the independent and shared effects of EPA, DPA and DHA

Omega-3 polyunsaturated fatty acids (PUFAs) exhibit neuroprotective properties and represent a potential treatment for a variety of neurodegenerative and neurological disorders. However, traditionally there has been a lack of discrimination between the different omega-3 PUFAs and effects have been broadly accredited to the series as a whole. Evidence for unique effects of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and more recently docosapentaenoic acid (DPA) is growing. For example, beneficial effects in mood disorders have more consistently been reported in clinical trials using EPA; whereas, with neurodegenerative conditions such as Alzheimer’s disease, the focus has been on DHA. DHA is quantitatively the most important omega-3 PUFA in the brain, and consequently the most studied, whereas the availability of high purity DPA preparations has been extremely limited until recently, limiting research into its effects. However, there is now a growing body of evidence indicating both independent and shared effects of EPA, DPA and DHA. The purpose of this review is to highlight how a detailed understanding of these effects is essential to improving understanding of their therapeutic potential. The review begins with an overview of omega-3 PUFA biochemistry and metabolism, with particular focus on the central nervous system (CNS), where DHA has unique and indispensable roles in neuronal membranes with levels preserved by multiple mechanisms. This is followed by a review of the different enzyme-derived anti-inflammatory mediators produced from EPA, DPA and DHA. Lastly, the relative protective effects of EPA, DPA and DHA in normal brain aging and the most common neurodegenerative disorders are discussed. With a greater understanding of the individual roles of EPA, DPA and DHA in brain health and repair it is hoped that appropriate dietary recommendations can be established and therapeutic interventions can be more targeted and refined.

Modulation of learning and memory by cytokines: signaling mechanisms and long term consequences

This review describes the role of cytokines and their downstream signaling cascades on the modulation of learning and memory. Immune proteins are required for many key neural processes and dysregulation of these functions by systemic inflammation can result in impairments of memory that persist long after the resolution of inflammation. Recent research has demonstrated that manipulations of individual cytokines can modulate learning, memory, and synaptic plasticity. The many conflicting findings, however, have prevented a clear understanding of the precise role of cytokines in memory. Given the complexity of inflammatory signaling, understanding its modulatory role requires a shift in focus from single cytokines to a network of cytokine interactions and elucidation of the cytokine-dependent intracellular signaling cascades. Finally, we propose that whereas signal transduction and transcription may mediate short-term modulation of memory, long-lasting cellular and molecular mechanisms such as epigenetic modifications and altered neurogenesis may be required for the long lasting impact of inflammation on memory and cognition.

Inflammation early in life is a vulnerability factor for emotional behavior at adolescence and for lipopolysaccharide-induced spatial memory and neurogenesis alteration at adulthood

BACKGROUND

The postnatal period is a critical time window during which inflammatory events have significant and enduring effects on the brain, and as a consequence, induce alterations of emotional behavior and/or cognition later in life. However, the long-term effect of neonatal inflammation on behavior during adolescence, a sensitive period for the development of neurodevelopmental psychiatric disorders, has been little studied. In this study, we examined whether an early-life inflammatory challenge could alter emotional behaviors and spatial memory at adolescence and adulthood and whether stress axis activity, inflammatory response and neurogenesis were affected.

METHODS

Lipopolysaccharide (LPS, 100 μg/kg) was administered to mice on postnatal day (PND) 14 and cytokine expression was measured in the plasma and in brain structures 3 hours later. Anxiety-like and depressive-like behavior (measured in the novelty-suppressed feeding test and the forced swim test, respectively) and spatial memory (Y-maze test) were measured at adolescence (PND30) and adulthood (PND90). Hypothalamic-pituitary-adrenal (HPA) axis activity (plasma corticosterone and glucocorticoid receptors in the hippocampus and prefrontal cortex) was measured at adulthood. In addition, the impact of a novel adult LPS challenge (100 μ/kg) was measured on spatial memory (Y-maze test), neurogenesis (doublecortin-positive cell numbers in the hippocampus) and plasma cytokine expression.

RESULTS

First, we show in PND14 pups that a peripheral administration of LPS induced the expression of pro- and anti-inflammatory cytokines in the plasma and brain structures that were studied 3 hours after administration. Anxiety-like behavior was altered in adolescent, but not in adult, mice, whereas depressive-like behavior was spared at adolescence and increased at adulthood. This was accompanied by a decreased phosphorylation of the glucocorticoid receptor in the prefrontal cortex, with no effect on corticosterone levels. Second, neonatal LPS treatment had no effect on spatial memory in adolescence and adulthood. However, a second challenge of LPS in adulthood impaired spatial memory performance and neurogenesis and increased circulating levels of CCL2.

CONCLUSIONS

Our study shows for the first time, in mice, that a peripheral LPS treatment at PND14 differentially alters emotional behaviors, but not spatial memory, at adolescence and adulthood. The behavioral effect of LPS at PND14 could be attributed to HPA axis deregulation and neurogenesis impairment.

What is microglia neurotoxicity (Not)?

Microglia most likely appeared early in evolution as they are not only present in vertebrates, but are also found in nervous systems of various nonvertebrate organisms. Mammalian microglia are derived from a specific embryonic, self-renewable myeloid cell population that is throughout lifetime not replaced by peripheral myeloid cells. These phylogenic and ontogenic features suggest that microglia serve vital functions. Yet, microglia often are described as neurotoxic cells, that actively kill (healthy) neurons. Since it is from an evolutionary point of view difficult to understand why an important and vulnerable organ like the brain should host numerous potential killers, we here review the concept of microglia neurotoxicity. On one hand it is discussed that most of our understanding about how microglia kill neurons is based on in vitro experiments or correlative staining studies that suffer from the difficulty to discriminate microglia and peripheral myeloid cells in the diseased brain. On the other hand it is described that a more functional approach by mutating, inactivating or deleting microglia is seldom associated with a beneficial outcome in an acute injury situation, suggesting that microglia are normally important protective elements in the brain. This might change in chronic disease or the aged brain, where; however, it remains to be established whether microglia simply lose their protective capacities or whether microglia become truly neurotoxic cells.

Chronic lipopolysaccharide exposure induces cognitive dysfunction without affecting BDNF expression in the rat hippocampus

Previous studies have shown that lipopolysaccharide (LPS) has the potential to cause cognitive dysfunction. However, the underlying pathogenesis has yet to be fully elucidated. Increasing attention is being focused on infection in the central nervous system. Therefore, the present study aimed to investigate the behavioral performance of rats receiving intraperitoneal injections of LPS and to determine the expression levels of amyloid-β (Aβ), brain-derived neurotrophic factor (BDNF) and pro-inflammatory cytokines in the hippocampus. In total, 30 male Wistar rats were randomly divided into 3 groups (each n=10): Control and 3 and 7 day LPS administration groups. The rats were intraperitoneally injected with saline or LPS for 3 or 7 days. Following this, rats performed the Morris water maze test, in which the latency to the platform and proportion of time spent in the target quadrant were recorded. Rats were then sacrificed and the hippocampi were harvested for determination of interleukin (IL)-1β, IL-6, tumor necrosis factor-α (TNF-α), Aβ and BDNF expression levels. LPS administration for 3 and 7 days significantly increased the latency to the platform and decreased the proportion of time spent in the target quadrant compared with those in the control group, (P<0.05). Administration of LPS for 3 and 7 days induced statistically significant increases in the expression levels of IL-1β, IL-6 and TNF-α in the hippocampus, compared with those in the control group (P<0.05). Additionally, the administration of LPS for 7 days induced a statistically significant increase in the expression level of Aβ in the hippocampus, compared with that in the control group (P<0.05). However, the administration of LPS did not elicit a statistically significant change in the expression level of BDNF in the hippocampus, compared with that in the control group (P>0.05). The results indicate that LPS induces cognitive dysfunction, which is associated with increased expression levels of pro-inflammatory cytokines and Aβ, but does not affect the expression of BDNF in the hippocampus.

Review: microglia of the aged brain: primed to be activated and resistant to regulation

Innate immunity within the central nervous system (CNS) is primarily provided by resident microglia. Microglia are pivotal in immune surveillance and also facilitate the co-ordinated responses between the immune system and the brain. For example, microglia interpret and propagate inflammatory signals that are initiated in the periphery. This transient microglial activation helps mount the appropriate physiological and behavioural response following peripheral infection. With normal ageing, however, microglia develop a more inflammatory phenotype. For instance, in several models of ageing there are increased pro-inflammatory cytokines in the brain and increased expression of inflammatory receptors on microglia. This increased inflammatory status of microglia with ageing is referred to as primed, reactive or sensitized. A modest increase in the inflammatory profile of the CNS and altered microglial function in ageing has behavioural and cognitive consequences. Nonetheless, there are major differences in microglial biology between young and old age when the immune system is challenged and microglia are activated. In this context, microglial activation is amplified and prolonged in the aged brain compared with adults. The cause of this amplified microglial activation may be related to impairments in several key regulatory systems with age that make it more difficult to resolve microglial activation. The consequences of impaired regulation and microglial hyper-activation following immune challenge are exaggerated neuroinflammation, sickness behaviour, depressive-like behaviour and cognitive deficits. Therefore the purpose of this review is to discuss the current understanding of age-associated microglial priming, consequences of priming and reactivity, and the impairments in regulatory systems that may underlie these age-related deficits.

Interleukin-1β inhibits the differentiation of hippocampal neural precursor cells into serotonergic neurons

Interleukin-1 beta (IL-1β) is one of pro-inflammatory cytokines. Recent studies have shown that IL-1β impairs hippocampal neurogenesis, mediates proliferation and differentiation of multipotent neural precursor cells (NPCs), and exerts effects of anti-proliferation, anti-neurogenesis, and pro-gliogenesis on embryonic hippocampal NPCs. The aim of this study was to examine the effect of IL-1β on the differentiation of hippocampal NPCs into functional serotonergic neurons, which play important roles in the pathophysiology and treatment of depression. Hippocampal NPCs were prepared from the hippocampus of neonatal rats (within 24h after birth). After three passages and phenotyping, hippocampal NPCs were cultured in a differentiating medium with various concentrations (5, 10, and 20 ng/mL) of IL-1β for 7 days. At the endpoint, the serotonergic differentiation of hippocampal NPCs in IL-1β-treated cultures decreased in a dose-dependent manner and this effect was blocked by IL-1ra, an IL-1 receptor antagonist capable of blocking the effects of IL-1 by binding to the same receptor (IL-1R1) without triggering signaling; serotonin in the lysate of the differentiated hippocampal NPCs decreased in IL-1β-treated cultures; and levels of Bcl-2 and phosphorylated extracellular-regulated kinase (pERK) were also lower in differentiated hippocampal NPCs with IL-1β treatment. These results support the hypothesis that IL-1β is an important factor in the stress-associated neuropathology and psychopathology and has relevance to the treatment of depressive symptoms in patients with depression.

n-3 Polyunsaturated fatty acids in animal models with neuroinflammation

Neuroinflammation is present in the majority of acute and chronic neurological disorders. Excess or prolonged inflammation in the brain is thought to exacerbate neuronal damage and loss. Identifying modulators of neuroinflammation is an active area of study since it may lead to novel therapies. Omega-3 polyunsaturated fatty acids (n-3 PUFA) are anti-inflammatory in many non-neural tissues; their role in neuroinflammation is less studied. This review summarizes the relationship between n-3 PUFA and brain inflammation in animal models of brain injury and aging. Evidence by and large shows protective effects of n-3 PUFA in models of sickness behavior, stroke, aging, depression, Parkinson's disease, diabetes, and cytokine- and irradiation-induced cognitive impairments. However, rigorous studies that test the direct effects of n-3 PUFA in neuroinflammation in vivo are lacking. Future research in this area is necessary to determine if, and if so which, n-3 PUFA directly target brain inflammatory pathways. n-3 PUFA bioactive metabolites may provide novel therapeutic targets for neurological disorders with a neuroinflammatory component.

Regionally distinct responses of microglia and glial progenitor cells to whole brain irradiation in adult and aging rats

Radiation therapy has proven efficacy for treating brain tumors and metastases. Higher doses and larger treatment fields increase the probability of eliminating neoplasms and preventing reoccurrence, but dose and field are limited by damage to normal tissues. Normal tissue injury is greatest during development and in populations of proliferating cells but also occurs in adults and older individuals and in non-proliferative cell populations. To better understand radiation-induced normal tissue injury and how it may be affected by aging, we exposed young adult, middle-aged, and old rats to 10 Gy of whole brain irradiation and assessed in gray- and white matter the responses of microglia, the primary cellular mediators of radiation-induced neuroinflammation, and oligodendrocyte precursor cells, the largest population of proliferating cells in the adult brain. We found that aging and/or irradiation caused only a few microglia to transition to the classically “activated” phenotype, e.g., enlarged cell body, few processes, and markers of phagocytosis, that is seen following more damaging neural insults. Microglial changes in response to aging and irradiation were relatively modest and three markers of reactivity - morphology, proliferation, and expression of the lysosomal marker CD68- were regulated largely independently within individual cells. Proliferation of oligodendrocyte precursors did not appear to be altered during normal aging but increased following irradiation. The impacts of irradiation and aging on both microglia and oligodendrocyte precursors were heterogeneous between white- and gray matter and among regions of gray matter, indicating that there are regional regulators of the neural response to brain irradiation. By several measures, the CA3 region of the hippocampus appeared to be differentially sensitive to effects of aging and irradiation. The changes assessed here likely contribute to injury following inflammatory challenges like brain irradiation and represent important end-points for analysis in studies of therapeutic strategies to protect patients from neural dysfunction.

Mitochondrial dysfunction and oxidative stress activate inflammasomes: impact on the aging process and age-related diseases

Oxidative stress and low-grade inflammation are the hallmarks of the aging process and are even more enhanced in many age-related degenerative diseases. Mitochondrial dysfunction and oxidative stress can provoke and potentiate inflammatory responses, but the mechanism has remained elusive. Recent studies indicate that oxidative stress can induce the assembly of multiprotein inflammatory complexes called the inflammasomes. Nod-like receptor protein 3 (NLRP3) is the major immune sensor for cellular stress signals, e.g., reactive oxygen species, ceramides, and cathepsin B. NLRP3 activation triggers the caspase-1-mediated maturation of the precursors of IL-1β and IL-18 cytokines. During aging, the autophagic clearance of mitochondria declines and dysfunctional mitochondria provoke chronic oxidative stress, which disturbs the cellular redox balance. Moreover, increased NF-κB signaling observed during aging could potentiate the expression of NLRP3 and cytokine proforms enhancing the priming of NLRP3 inflammasomes. Recent studies have demonstrated that NLRP3 activation is associated with several age-related diseases, e.g., the metabolic syndrome. We will review here the emerging field of inflammasomes in the appearance of the proinflammatory phenotype during the aging process and in age-related diseases.

Investigating the role of zinc in a rat model of epilepsy

AIMS

The aim of the present study was to investigate the role of zinc (Zn) in pilocarpine-induced seizures and its interrelation with an antiepileptic drug, namely, valproic acid.

METHODOLOGY

The study was carried out on 110 male Wistar albino rats that were divided into the following groups: Group I, control rats that received intraperitoneal (i.p.) saline vehicle; Groups II-V received Zn in a medium dose, Zn in a high dose, valproic acid in a therapeutic dose, as well as a combination of valproic acid with medium dose Zn, respectively, for 3 weeks before saline injection, Group VI received i.p. pilocarpine to induce seizures; Groups VII-XI received Zn in a medium dose, Zn in a high dose, valproic acid in a therapeutic dose, a combination of therapeutic dose of valproic acid with medium dose Zn, as well as a combination of subeffective dose of valproic acid with medium dose of Zn, respectively, for 3 weeks before pilocarpine injection. The seizure's latency and severity for each rat was recorded. Blood and brain hippocampal samples were collected for determination of serum neuron specific enolase (NSE), hippocampal Zn, interleukin-1 beta concentrations as well as hippocampal superoxide dismutase and caspase-3 activities.

RESULTS

The results of the current study demonstrated that pretreatment with high dose of Zn exacerbated pilocarpine-induced seizures. Whereas, a medium dose of Zn and valproic acid either alone or in combination reduced the severity of pilocarpine-induced limbic seizures and increased the latency to attain the forelimb clonus. Also both drugs, either alone or in combination, ameliorated all studied biochemical parameters with the exception of hippocampal Zn concentration, which was only significantly increased by pretreatment with Zn, either alone or in combination with valproic acid.

CONCLUSIONS

The present study highlights the antiepileptic role that could be played by Zn, when given in appropriate doses.

Fractalkine-induced activation of the phosphatidylinositol-3 kinase pathway attentuates microglial activation in vivo and in vitro

Several neurodegenerative disorders are associated with evidence of inflammation, one feature of which is increased activation of microglia, the most likely cellular source of inflammatory cytokines like interleukin-1beta. It is now recognized that interaction of microglia with other cells contributes to maintenance of microglia in a quiescent state and the complementary distribution of the chemokine, fractalkine (CX(3)CL1) on neurons and its receptor (CX(3)CR1) on microglia, suggests that this interaction may play a role in modulating microglial activation. Here we demonstrate that both soluble and membrane-bound fractalkine attenuate lipopolysaccharide-induced microglial activation in vitro. We also show that fractalkine expression is reduced in the brain of aged rats and this is accompanied by an age-related increase in microglial activation. Treatment of aged rats with fractalkine attenuates the age-related increase in microglial activation and the evidence indicates that fractalkine-induced activation of the phosphatidylinositol-3 kinase pathway is required to maintain microglia in a quiescent state both in vivo and in vitro.

Immune and behavioral consequences of microglial reactivity in the aged brain

Bidirectional communication between the immune system and the brain is essential for mounting the appropriate immunological, physiological, and behavioral responses to immune activation. Aging, however, may impair this important bi-directional interaction. In support of this notion, peripheral infection in the elderly is associated with an increased frequency of behavioral and cognitive complications. Recent findings in animal models of aging and neurodegenerative disease indicate that microglia, innate immune cells of the brain, become primed or reactive. Understanding age- and disease-associated alterations in microglia is important because glia (microglia and astrocytes) play an integral role in propagating inflammatory signals that are initiated in the periphery. In this capacity, brain glia produce inflammatory cytokines that target neuronal substrates and elicit a sickness-behavior syndrome that is normally beneficial to the host organism. Increased reactivity of microglia sets the stage for an exaggerated neuroinflammatory cytokine response following activation of the peripheral innate immune system, which may underlie subsequent long-lasting behavioral and cognitive deficits. In support of this premise, recent findings indicate that stimulation of the peripheral immune system in aged rodents causes exaggerated neuroinflammation that is paralleled by cognitive impairment, prolonged sickness, and depressive-like complications. Therefore, the purpose of this review is to discuss the new evidence that age-associated priming of microglia could play a pathophysiological role in exaggerated behavioral and cognitive sequelae to peripheral infection.

Effects of eicosapentaenoic acid on synaptic plasticity, fatty acid profile and phosphoinositide 3-kinase signaling in rat hippocampus and differentiated PC12 cells

Placebo-controlled clinical studies suggest that intake of n-3 polyunsaturated fatty acids improves neurological disorders such as Alzheimer's disease, Huntington's disease and schizophrenia. To evaluate the impact of eicosapentaenoic acid (EPA), we orally administered highly purified ethyl EPA (EPA-E) to rats at a dose of 1.0 mg/g per day and measured long-term potentiation of the CA1 hippocampal region, a physiological correlate of synaptic plasticity that is thought to underlie learning and memory. The mean field excitatory postsynaptic potential slope of the EPA-E group was significantly greater than that of the control group in the CA1 region. Gene expression of hippocampal p85alpha, one of the regulatory subunits of phosphatidylinositol 3-kinase (PI3-kinase), was increased with EPA-E administration. Investigation of fatty acid profiles of neuronal and glia-enriched fractions demonstrated that a single administration of EPA-E significantly increased neuronal and glial EPA content and glial docosahexaenoic acid content, clearly suggesting that EPA was indeed taken up by both neurons and glial cells. In addition, we investigated the direct effects of EPA on the PI3-kinase/Akt pathway in differentiated PC12 cells. Phosphorylated-Akt expression was significantly increased in EPA-treated cells, and nerve growth factor withdrawal-induced increases in cell death and caspase-3 activity were suppressed by EPA treatment. These findings suggest that EPA protects against neurodegeneration by modulating synaptic plasticity and activating the PI3-kinase/Akt pathway, possibly by its own functional effects in neurons and glial cells and by its capacity to increase brain docosahexaenoic acid.

Peripheral lipopolysaccharide (LPS) challenge promotes microglial hyperactivity in aged mice that is associated with exaggerated induction of both pro-inflammatory IL-1beta and anti-inflammatory IL-10 cytokines

In the elderly, systemic infection is associated with an increased frequency of behavioral and cognitive complications. We have reported that peripheral stimulation of the innate immune system with lipopolysaccharide (LPS) causes an exaggerated neuroinflammatory response and prolonged sickness/depressive-like behaviors in aged BALB/c mice. Therefore, the purpose of this study was to determine the degree to which LPS-induced neuroinflammation was associated with microglia-specific induction of neuroinflammatory mediators. Here, we show that peripheral LPS challenge caused a hyperactive microglial response in the aged brain associated with higher induction of inflammatory IL-1beta and anti-inflammatory IL-10. LPS injection caused a marked induction of mRNA expression of both IL-1beta and IL-10 in the cortex of aged mice compared to adults. In the next set of studies, microglia (CD11b(+)/CD45(low)) were isolated from the brain of adult and aged mice following experimental treatments. An age-dependent increase in major histocompatibility complex (MHC) class II mRNA and protein expression was detected in microglia. Moreover, peripheral LPS injection caused a more pronounced increase in IL-1beta, IL-10, Toll-like receptor (TLR)-2, and indoleamine 2,3-dioxygenase (IDO) mRNA levels in microglia isolated from aged mice than adults. Intracellular cytokine protein detection confirmed that peripheral LPS caused the highest increase in IL-1beta and IL-10 levels in microglia of aged mice. Finally, the most prominent induction of IL-1beta was detected in MHC II(+) microglia from aged mice. Taken together, these findings provide novel evidence that age-associated priming of microglia plays a central role in exaggerated neuroinflammation induced by activation of the peripheral innate immune system.

Neuroprotective effect of sodium ferulate and signal transduction mechanisms in the aged rat hippocampus

AIM

To investigate whether the age-related increase in interleukin-1beta (IL-1beta) and c-Jun N-terminal kinases (JNK) pathway was coupled with a decrease in cell survival signaling pathways and whether sodium ferulate (SF) treatment was effective in preventing these age-associated changes.

METHODS

Groups of young and aged rats were fed for 4 weeks on a diet enriched in SF (100 mg/kg and 200 mg/kg per day). At the end of the period of dietary manipulation, Western blotting analysis was used to determine the expressions of IL-1beta, phosphorylated mitogen-activated protein kinase kinase (MKK)4, phospho-JNK, phospho-c-Jun, phosphorylated extracellular signal-regulated kinase (ERK1/2), phospho-MEK, phospho-Akt, phosphorylated ribosomal protein S6 protein kinase (p70S6K), and activated caspase-3 and caspase-7. Nissl staining was used to observe the morphological change in hippocampal CA1 regions. Immunohistochemical techniques for glial fibrillary acidic protein (GFAP) and integrin alphaM (OX-42) were used to determine the astrocyte and microglia activation.

RESULTS

IL-1beta protein levels, and phospho-MKK4, phospho-JNK1/2, and phospho-c-Jun were significantly enhanced in hippocampus prepared from age-matched control rats. Increased IL-1beta production and JNK1/2 activation was accompanied by downregulation of MEK/ERK1/2 pathway and Akt/p70S6K pathway, leading to cell apoptosis assessed by activation of caspase-3. Significantly, treatment of aged rats with SF (100 mg/kg and 200 mg/kg per day) for 4 weeks prevented the agerelated increase in IL-1beta and IL-1beta-induced JNK signaling pathway and also the age-related changes in ERK and Akt kinase.

CONCLUSION

SF plays neuroprotective roles through suppression of IL-1beta and IL-1beta-induced JNK signaling and upregulation of MEK/ERK1/2 and Akt/p70S6K survival pathways.

Early-life infection leads to altered BDNF and IL-1beta mRNA expression in rat hippocampus following learning in adulthood

Neonatal bacterial infection in rats leads to profound hippocampal-dependent memory impairments following a peripheral immune challenge in adulthood. Here, we determined whether neonatal infection plus an immune challenge in adult rats is associated with impaired induction of brain-derived neurotrophic factor (BDNF) within the hippocampus (CA1, CA3, and dentate gyrus) following fear conditioning. BDNF is well characterized for its critical role in learning and memory. Rats injected on postnatal day 4 with PBS (vehicle) or Escherichia coli received as adults either no conditioning or a single 2min trial of fear conditioning. Half of the rats in the conditioned group then received a peripheral injection of 25mug/kg lipopolysaccharide (LPS) and all were sacrificed 1 or 4h later. Basal (unconditioned) BDNF mRNA did not differ between groups. However, following conditioning, neonatal infection with E. coli led to decreased BDNF mRNA induction in all regions compared to PBS-treated rats. This decrease in E. coli-treated rats was accompanied by a large increase in IL-1beta mRNA in CA1. Taken together, these data indicate that early infection strongly influences the induction of IL-1beta and BDNF within distinct regions of the hippocampus, which likely contribute to observed memory impairments in adulthood.

Chronic mild stress impairs cognition in mice: from brain homeostasis to behavior

Exposure to chronic stress in rodents and psychosocial stress in humans has been shown to alter cognitive functions and has been linked to the pathophysiology of mood disorders. The purpose of the present study was to investigate effects and possible mechanisms of a chronic mild stress (CMS) procedure on cognitive behaviors in Swiss albino mice using the object recognition test (ORT) and object location test (OLT). Results showed that CMS exposure impaired cognitive performance and produced amnesia of acquired information in both ORT and OLT. Furthermore, the cognitive impairment was coexistent with increased plasma levels of interleukin-1beta (IL-1beta), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha), as well as with enhanced plasma levels of corticosterone (CORT), corticotrophin-releasing hormone (CRH) and adrenocorticotrophic hormone (ACTH). In addition, severe neuronal cell damage was found, as bromodeoxyuridine (BrdU) positive cells and the expression of brain derived neurotrophic factor (BDNF) in dentate gyrus (DG) of hippocampus were decreased after 5 weeks CMS procedure. Taken together, these findings indicated that CMS exposure-induced impairment of cognitive behaviors might be attributed to the stress-related alterations in brain homeostasis that were reflected in changes in the neuroimmune and neuroendocrine systems as well as in neurogenesis.

Morphological and biochemical signs of age-related neurodegenerative changes in klotho mutant mice

Klotho mutant mice, defective in the klotho gene, develop multiple age-related disorders with very short lifespans. Introduction of the exogenous klotho gene into these mutant mice leads to an improvement in their phenotypes, while overexpression of this gene in wild-type mice significantly extends their lifespan. These observations suggest that the klotho gene/protein has an anti-aging function. Since there have been only a few reports with some disagreement about results on the CNS of the mutant mice, we tried to clarify whether the CNS neurons generate aging-like features, even in premature stages, using biochemical and morphological approaches. Results obtained from the mutant mice, when compared with wild-type mice, were as follows. Neurofilaments (NFs) were increased significantly in axons, with the subunit proteins showing a significant enhancement in phosphorylation or expression of NF-H or NF-L, respectively. Microtubules in Purkinje cell dendrites were closer to each other, and in the CNS tissue tubulin was unaltered, but microtubule-associated protein (MAP) 2 was significantly reduced in expression. Neuronal cellular organelles were morphologically disordered. Lysosomes, cathepsin D and light chain 3 of MAP1A/B (LC3) were augmented with the appearance of putative autophagy-related structures. Antiapoptotic Bcl-xL and proapoptotic Bax were reduced and enhanced, respectively, and mitogen-activated protein kinase was reduced. Synapse-related proteins and structures were decreased. Neuronal degeneration was evident in hippocampal pyramidal cells, and possibly in Purkinje cells. Astrocytic glial filaments and glial fibrillary acidic protein were increased in density and expression, respectively. Together, the CNS neuronal alterations in klotho mutant mice were quite similar to those found in aged animals, including even premature death, so this mouse should be a more appropriate animal model for CNS aging than those previously reported.