The mosaic of brain glial hyperactivity during normal ageing and its attenuation by food restriction

Stress-evoked sterile inflammation, danger associated molecular patterns (DAMPs), microbial associated molecular patterns (MAMPs) and the inflammasome

Since the inception of the field of psychoneuroimmunolology research, there has been an appreciation that the physiological response to stressors includes modulation of immune function. Investigators initially focused on the effect of stress on cellular migration and immunosuppression and the resultant decreases in tumor surveillance, anti-viral T cell immunity and antigen-specific antibody responses. More recently, it has become clear that exposure to stressors also potentiate innate immune processes. Stressor exposure, for example, can change the activation status of myeloid lineage cells such as monocytes, macrophages, neutrophils, and microglia, leading to a primed state. In addition, stressor exposure increases the synthesis and release of a vast cadre' of inflammatory proteins both in the blood and within tissues (i.e., spleen, liver, adipose, vasculature and brain). The mechanisms for stress-evoked innate immune 'arousal' remain unknown. The goals of this presidential address are the following: (1) offer a personalized, brief overview of stress and immunity with a focus on 'aroused' innate immunity; (2) describe sterile inflammatory processes and the role of the inflammasome; and (3) suggest that these same processes likely contribute to primed myeloid cells and inflammatory protein responses (systemic and tissue) produced by stress in the absence of pathogens.

The neuron-astrocyte-microglia triad in normal brain ageing and in a model of neuroinflammation in the rat hippocampus

Ageing is accompanied by a decline in cognitive functions; along with a variety of neurobiological changes. The association between inflammation and ageing is based on complex molecular and cellular changes that we are only just beginning to understand. The hippocampus is one of the structures more closely related to electrophysiological, structural and morphological changes during ageing. In the present study we examined the effect of normal ageing and LPS-induced inflammation on astroglia-neuron interaction in the rat hippocampus of adult, normal aged and LPS-treated adult rats. Astrocytes were smaller, with thicker and shorter branches and less numerous in CA1 Str. radiatum of aged rats in comparison to adult and LPS-treated rats. Astrocyte branches infiltrated apoptotic neurons of aged and LPS-treated rats. Cellular debris, which were more numerous in CA1 of aged and LPS-treated rats, could be found apposed to astrocytes processes and were phagocytated by reactive microglia. Reactive microglia were present in the CA1 Str. Radiatum, often in association with apoptotic cells. Significant differences were found in the fraction of reactive microglia which was 40% of total in adult, 33% in aged and 50% in LPS-treated rats. Fractalkine (CX3CL1) increased significantly in hippocampus homogenates of aged and LPS-treated rats. The number of CA1 neurons decreased in aged rats. In the hippocampus of aged and LPS-treated rats astrocytes and microglia may help clearing apoptotic cellular debris possibly through CX3CL1 signalling. Our results indicate that astrocytes and microglia in the hippocampus of aged and LPS-infused rats possibly participate in the clearance of cellular debris associated with programmed cell death. The actions of astrocytes may represent either protective mechanisms to control inflammatory processes and the spread of further cellular damage to neighboring tissue, or they may contribute to neuronal damage in pathological conditions.

Age-changes in gene expression in primary mixed glia cultures from young vs. old rat cerebral cortex are modified by interactions with neurons

Astrocytic GFAP expression increases during normal aging in many brain regions and in primary astrocyte cultures derived from aging rodent brains. As shown below, we unexpectedly found that the age-related increase of GFAP expression was suppressed in mixed glia (astrocytes+microglia). However, the age-related increase of GFAP was observed when E18 neurons were co-cultured with mixed glia. Thus, the presence of microglia can suppress the age-related increase of GFAP, in primary cultures of astrocytes. To more broadly characterize how aging and co-culture with neurons alters glial gene expression, we profiled gene expression in mixed glia from young (3 mo) and old (24 mo) male rat cerebral cortex by Affymetrix microarray (Rat230 2.0). The majority of age changes were independent of the presence of neurons. Overall, the expression of twofold more genes increased with age than decreased with age. The minority of age changes that were either suppressed or revealed by the presence of neurons may be useful to analyze glial-neuron interaction during aging. Some in vitro changes are shared with those of aging rat hippocampus in studies from the Landfield group (Rowe et al., 2007; Kadish et al., 2009).

Dementia in Parkinson's Disease Correlates with α-Synuclein Pathology but Not with Cortical Astrogliosis

Dementia is a common feature in Parkinson's disease (PD) and is considered to be the result of limbic and cortical Lewy bodies and/or Alzheimer changes. Astrogliosis may also affect the development of dementia, since it correlates well with declining cognition in Alzheimer patients. Thus, we determined whether cortical astrogliosis occurs in PD, whether it is related to dementia, and whether this is reflected by the presence of glial fibrillary acidic protein (GFAP) and vimentin in cerebrospinal fluid (CSF). We have examined these proteins by immunohistochemistry in the frontal cortex and by Western blot in CSF of cases with PD, PD with dementia (PDD), dementia with Lewy bodies (DLB) and nondemented controls. We were neither able to detect an increase in cortical astrogliosis in PD, PDD, or DLB nor could we observe a correlation between the extent of astrogliosis and the degree of dementia. The levels of GFAP and vimentin in CSF did not correlate to the extent of astrogliosis or dementia. We did confirm the previously identified positive correlation between the presence of cortical Lewy bodies and dementia in PD. In conclusion, we have shown that cortical astrogliosis is not associated with the cognitive decline in Lewy body-related dementia.

Clusterin in Alzheimer's disease

Clusterin, also known as apolipoprotein J, is a ubiquitous multifunctional glycoprotein. Following its identification in 1983, clusterin was found to be clearly increased in Alzheimer's disease (AD). Later research demonstrated that clusterin could bind amyloid-beta (Abeta) peptides and prevent fibril formation, a hallmark of AD pathology. In addition to preventing excessive inflammation, intracellular clusterin was found to reduce apoptosis and oxidative stress. Although early studies were inconclusive, two recent large-scale genome-wide association studies (GWAS) independently identified variants within the clusterin gene as risk factors for developing AD. This review focuses on the characteristics of clusterin and possible mechanisms of its relationship to AD.

High caloric intake, poor cognition and dementia: the Caerphilly Prospective Study

To examine the hypothesis that caloric intake in mid-life is associated with later dementia or cognitive impairment not dementia (CIND). A prospective cohort study was conducted in Caerphilly, South Wales, United Kingdom. Men aged 45-59 years were identified from the electoral roll and general practice. 2,512 men were examined between July 1979 until September 1983. Four follow-up examinations were conducted every 4-5 years until 2004. Participants were categorized on the basis of their average daily caloric intake over each of the first three phases. Outcomes were CIND and dementia ascertained at phase five (2004). 192 men (15% of 1,248 participants at phase five) had CIND and 100 (8%) dementia. Age adjusted odds ratios demonstrated strongest associations between average energy consumption and vascular CIND or dementia (OR 1.62 95% CI 1.25-2.10). Adjustment for nutritional factors, vascular disease, diabetes, smoking, BP and BMI if anything increased the association (OR 1.64, 95% CI 1.03-2.60). After adjusting for social class, associations were attenuated and consistent with chance (OR 1.48, 95% CI 0.92-2.38). When adjusted for social class, the previously observed association between caloric intake and cognitive outcomes is modest, consistent with chance, and may be due to residual confounding.

Differential responses of progesterone receptor membrane component-1 (Pgrmc1) and the classical progesterone receptor (Pgr) to 17β-estradiol and progesterone in hippocampal subregions that support synaptic remodeling and neurogenesis

Progesterone (P4) and estradiol (E2) modulate neurogenesis and synaptic remodeling in the hippocampus during the rat estrous cycle and in response to deafferenting lesions, but little is known about the steroidal regulation of hippocampal progesterone receptors associated with these processes. We examined the neuronal expression of progesterone receptor membrane component-1 (Pgrmc1) and the classical progesterone receptor (Pgr), by in situ hybridization and immunohistochemistry. Pgr, a transcription factor, has been associated with synaptic remodeling and other major actions of P4, whereas Pgrmc1 is implicated in P4-dependent proliferation of adult neuroprogenitor cells and with rapid P4 effects on membranes. Ovariectomized adult rats were given E2, P4, or E2+P4 on two schedules: a 4-d model of the rodent estrous cycle and a 30-d model of postmenopausal hormone therapy. Pgr was hormonally responsive only in CA1 pyramidal neurons, and the induction of Pgr by E2 was partly antagonized by P4 only on the 30-d schedule. In CA3 pyramidal and dentate gyrus (DG) neurons, Pgr was largely unresponsive to all hormone treatments. In contrast to Pgr, Pgrmc1 was generally induced by E2 and/or P4 throughout the hippocampus in CA1, CA3, and DG neurons. In neuroprogenitor cells of the DG (immunopositive for bromodeoxyuridine and doublecortin), both Pgrmc1 and Pgr were detected. The differential regulation of hippocampal Pgrmc1 and Pgr by E2 and P4 may guide drug development in hormonal therapy for support of neurogenesis and synaptic regeneration.

Aging microglia: relevance to cognition and neural plasticity

Over the years it has become evident that the immune system can affect the function of the central nervous system (CNS), including altering cognitive processes. The impact of immune activation on the CNS is particularly important for aged individuals, as the brain's resident immune cells, microglia, acquire a pro-inflammatory profile. The low-grade chronic neuroinflammation that develops with normal aging likely contributes to the susceptibility to cognitive deficits and a host of age-related pathologies. Understanding why microglia show increased inflammatory activity (i.e., neuroinflammation) and identifying effective treatments to reduce microglia activation is expected to have beneficial effects on cognitive performance and measures of neural plasticity. However, microglia also promote regeneration after injury. Therefore, effective treatments must dampen inflammatory activity while preserving microglia's neuroprotective function. Discovering factors that induce neuroinflammation and investigating potential preventative therapies is expected to uncover the ways of maintaining normal microglia activity in the aged brain.

Effect of growth hormone and melatonin on the brain: from molecular mechanisms to structural changes

Aging of the brain causes important reductions in quality of life and has wide socio-economic consequences. An increase in oxidative stress, and the associated inflammation and apoptosis, could be responsible for the pathogenesis of aging associated brain lesions. Melatonin has neuroprotective effects, by limiting the negative effects of oxygen and nitrogen free radicals. Growth hormone (GH) might exert additional neuro-protective and or neurogenic effects on the brain. The molecular mechanisms of the protective effects of GH and melatonin on the aging brain have been investigated in young and old Wistar rats. A reduction in the total number of neurons in the hilus of the dentate gyrus was evident at 24 months of age and was associated with a significant increase in inflammation markers as well as in pro-apoptotic parameters, confirming the role of apoptosis in its reduction. Melatonin treatment was able to enhance neurogenesis in old rats without modification of the total number of neurons, whereas GH treatment increased the total number of neurons without enhancing neurogenesis. Both GH and melatonin were able to reduce inflammation and apoptosis in the hippocampus. In conclusion, neuroprotective effects demonstrated by GH and melatonin in the hippocampus were exerted by decreasing inflammation and apoptosis.

Cognitive and behavioral consequences of impaired immunoregulation in aging

A hallmark of the aged immune system is impaired immunoregulation of the innate and adaptive immune system in the periphery and also in the central nervous system (CNS). Impaired immunoregulation may predispose older individuals to an increased frequency of peripheral infections with concomitant cognitive and behavioral complications. Thus, normal aging is hypothesized to alter the highly coordinated interactions between the immune system and the brain. In support of this notion, mounting evidence in rodent models indicate that the increased inflammatory status of the brain is associated with increased reactivity of microglia, the innate immune cells of the CNS. Understanding how immunity is affected with age is important because CNS immune cells play an integral role in propagating inflammatory signals that are initiated in the periphery. Increased reactivity of microglia sets the stage for an exaggerated inflammatory cytokine response following activation of the peripheral innate immune system that is paralleled by prolonged sickness, depressive-like complications and cognitive impairment. Moreover, amplified neuroinflammation negatively affects several aspects of neural plasticity (e.g., neurogenesis, long-term potentiation, and dendritic morphology) that can contribute to the severity of neurological complications. The purpose of this review is to discuss several key peripheral and central immune changes that impair the coordinated response between the immune system and the brain and result in behavioral and cognitive deficits.

Age-associated development of inflammation in Wistar rats: Effects of caloric restriction

CONTEXT

Insulin resistance and type 2 Diabetes have been associated to a low grade of inflammation and their prevalence increase with ageing.

OBJECTIVE

To analyse the development of inflammation in adipose tissue, liver, muscle and hypothalamus during ageing and the effects of caloric restriction.

MATERIALS AND METHODS

We have analysed the expression of inflammatory cytokines (TNFα, IL1-β, IL-12B and IL-6), proteins involved in macrophage recruitment (MCP-1, CCR2), TLR4 and macrophage markers (CD11c, CD11b and arginase1). Immunohistochemistry of macrophages has also been performed.

RESULTS

All studied tissues present signs of inflammation during ageing, but with different pattern and intensity. Caloric restriction decreases the expression of most of inflammatory markers.

DISCUSSION AND CONCLUSIONS

These data indicate a role of adiposity in the development of inflammation and insulin resistance during ageing. Dietetic intervention could be a useful tool to ameliorate the development of inflammation and insulin resistance associated with ageing.

Glial transcripts and immune-challenged glia in the suprachiasmatic nucleus of young and aged mice

Biological rhythms are frequently disturbed with advancing age, and aging-related changes of glia in the hypothalamic suprachiasmatic nucleus (SCN), the master circadian pacemaker, require special attention. In particular, astrocytes contribute to SCN function, and aging is associated with increased inflammatory activity in the brain, in which microglia could be especially implicated. On this basis, we investigated in the SCN of young and old mice glial transcripts and cell features, and the glial cell response to a central inflammatory challenge. Quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) was used to analyze the expression of mRNAs encoding the astrocytic glial fibrillary acidic protein and the microglial antigen CD11b. Both these transcripts, here investigated in the SCN for the first time, were significantly increased in the old SCN. Glial cell phenotyping with immunohistochemistry revealed hypertrophic and intensely stained astrocytes and microglia in the aged SCN. In both age groups, microglia were scattered throughout the SCN and astrocytes were prominent in the ventral portion, where retinal fibers are densest; in the aged SCN, astrocytes were also numerous in the dorsal portion. After intracerebroventricular injections of a mixture of interferon-gamma and tumor necrosis factor-alpha, or phosphate-buffered saline as control, immunolabeling was evaluated with stereological cell counts and confocal microscopy. Phenotypic features of astrocyte and microglia activation in response to cytokine injections were markedly enhanced in the aged SCN. Subregional variations in glial cell density were also documented in the aged compared to the young SCN. Altogether, the findings show increases in the expression of glial transcripts and hypertrophy of astrocytes and microglia in the aged SCN, as well as age-dependent variation in the responses of immune-challenged SCN glia. The data thus point out an involvement of glia in aging-related changes of the biological clock.

Neuronutrition and Alzheimer's disease

Alzheimer's disease (AD) is a complex neurological disorder resulting from both genetic and environmental factors with the latter being particularly important for the sporadic form of the disease. As such, diets rich in saturated fatty acids and alcohol, and deficient in antioxidants and vitamins appear to promote the onset of the disease, while diets rich in unsaturated fatty acids, vitamins, antioxidants, and wine likely suppress its onset. In addition, evidence suggests that diets rich in polyphenols and some spices suppress the onset of AD by scavenging free radicals and preventing oxidative damage. Metal ions are known to catalyze the production of free radicals and induce mental retardation or dementia, and several studies have also identified metals such as Pb, Fe, Al, Cu, and Zn in AD pathogenesis. While specific metal chelators have been tested for therapy, they have not been very successful, probably due to their late administration, i.e., after brain damage has been triggered. Since several dietary polyphenols are known to chelate metals, their routine use may also be protective against the onset of AD. In this review, we summarize beneficial dietary techniques in the fight against AD.

Restricted ketogenic diet enhances the therapeutic action of N-butyldeoxynojirimycin towards brain GM2 accumulation in adult Sandhoff disease mice

Sandhoff disease is an autosomal recessive, neurodegenerative disease involving the storage of brain ganglioside GM2 and asialo-GM2. Previous studies showed that caloric restriction, which augments longevity, and N-butyldeoxynojirimycin (NB-DNJ, Miglustat), an imino sugar that hinders the glucosyltransferase catalyzing the first step in glycosphingolipid biosynthesis, both increase longevity and improve motor behavior in the beta-hexosaminidase (Hexb) knockout (-/-) murine model of Sandhoff disease. In this study, we used a restricted ketogenic diet (KD-R) and NB-DNJ to combat ganglioside accumulation. Adult Hexb-/- mice were placed into one of the following groups: (i) a standard diet (SD), (ii) a SD with NB-DNJ (SD + NB-DNJ), (iii) a KD-R, and (iv) a KD-R with NB-DNJ (KD-R + NB-DNJ). Forebrain GM2 content (mug sialic acid/100 mg dry wt) in the four groups was 375 +/- 15, 312 +/- 8, 340 +/- 28, and 279 +/- 26, respectively, indicating an additive interaction between NB-DNJ and the KD-R. Most interestingly, brain NB-DNJ content was 3.5-fold greater in the KD-R + NB-DNJ mice than in the SD + NB-DNJ mice. These data suggest that the KD-R and NB-DNJ may be a potential combinatorial therapy for Sandhoff disease by enhancing NB-DNJ delivery to the brain and may allow lower dosing to achieve the same degree of efficacy as high dose monotherapy.

Clusterin: a forgotten player in Alzheimer's disease

Clusterin, also known as apolipoprotein J, is a versatile chaperone molecule which contains several amphipathic and coiled-coil alpha-helices, typical characteristics of small heat shock proteins. In addition, clusterin has three large intrinsic disordered regions, so-called molten globule domains, which can stabilize stressed protein structures. Twenty years ago, it was demonstrated that the expression of clusterin was clearly increased in Alzheimer's disease (AD). Later it was observed that clusterin can bind amyloid-beta peptides and prevent their fibrillization. Clusterin is also involved in the clearance of amyloid-beta peptides and fibrils by binding to megalin receptors and enhancing their endocytosis within glial cells. Clusterin is a complement inhibitor and can suppress complement activation observed in AD. Clusterin is also present in lipoprotein particles and regulates cholesterol and lipid metabolism of brain which is disturbed in AD. Clusterin is a stress-induced chaperone which is normally secreted but in conditions of cellular stress, it can be transported to cytoplasm where it can bind to Bax protein and inhibit neuronal apoptosis. Clusterin can also bind to Smad2/3 proteins and potentiate the neuroprotective TGFbeta signaling. An alternative splicing can produce a variant isoform of clusterin which can be translocated to nuclei where it induces apoptosis. The role of nuclear clusterin in AD needs to be elucidated. We will review here the extensive literature linking clusterin to AD and examine the recent progress in clusterin research with the respect to AD pathology. Though clusterin can be viewed as a multipotent guardian of brain, it is unable to prevent the progressive neuropathology in chronic AD.

Age and neuroinflammation: a lifetime of psychoneuroimmune consequences

Aging can impair functional interaction that occurs between the brain and the immune system. Recent findings indicate that microglia and astrocytes, innate immune cells of the brain, become more reactive during normal aging. This age-associated increase in innate immune reactivity sets the stage for an exaggerated inflammatory cytokine response in the brain after activation of the peripheral innate immune system. This elevated neuroinflammatory response may lead to more severe long-lasting behavioral and cognitive deficits. This article discusses new evidence that aging creates a brain environment that is permissive to the occurrence of mental health complications following innate immune activation.

Ladostigil prevents age-related glial activation and spatial memory deficits in rats

Oxidative stress and glial activation occur in the aging brain. Ladostigil is a new monoamine oxidase (MAO) and acetylcholinesterase (AChE) inhibitor designed for the treatment of Alzheimer's disease. It has neuroprotective and antioxidant activities in cellular models at much lower concentrations than those inhibiting MAO or AChE. When ladostigil (1mg/kg/day) was given for 6 months to 16-month-old rats it prevented the age-related increase in activated astrocytes and microglia in several hippocampal and white matter regions and increased proNGF immunoreactivity in the hippocampus towards the levels in young rats. Ladostigil also prevented the age-related reduction in cortical AChE activity and the increase in butyrylcholinesterase activity in the hippocampus, in association with the reduction in gliosis. The immunological and enzymatic changes in aged rats were associated with improved spatial memory. Ladostigil treatment had no effect on memory, glial or proNGF immunoreactivity in young rats. Early treatment with ladostigil could slow disease progression in conditions like Alzheimer's disease in which oxidative stress and inflammatory processes are present.

Changes of autologous neural stem cells in the hippocampi of aging mice

Although there is possibility of cognitive disturbance in aging people, many of them live for long life and enjoy well-functioning brain during the whole life-span. The biological basis of longevity is unknown. In this study, we investigated the influence of aging on hippocampal neural stem cells (NSCs), and the correlations between hippocampal neurogenesis and cognitive function. The result showed that the protein production and mRNA expression of nestin, and the number of BrdU(+) cells in dentate gyrus (DG) of the aged non-dementia mice were clearly higher than that in the aged dementia mice and the young adult mice. We also found that the number of NeuN(+) (neuron-specific nuclear antigen) cells in DG and CA1, choline O-acetyltransferase (ChAT, EC 2.3.1.6) production and mRNA expression in hippocampi of the aged-dementia mice were significantly reduced as compared to that of the young adult mice and the aged non-dementia mice, whereas the number of NeuN(+) cells, ChAT production and mRNA expression of the aged non-dementia mice has no difference with that of the young adult mice. Glial fibrillary acidic protein (GFAP) expression in the hippocampi of aged dementia mice significantly higher than that of the young adult mice and the aged non-dementia mice. Our results suggest that aging sometimes does not cause changing of the number of neurons and the hippocampal neurogenesis. Increment of DNA replication and neuron replacement, promotion of differentiation of neural stem cells, enhancement of neuronal proliferation, facilitation of synaptic plasticity of neurons may all benefit to the maintenance of the normal cognitive ability in the aged mice.

Behavioral and histological assessment of the effect of intermittent feeding in the pilocarpine model of temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is the most resistant type of epilepsy. Currently available drugs for epilepsy are not antiepileptogenic. A novel treatment for epilepsy would be to block or reverse the process of epileptogenesis. We used intermittent feeding (IF) regimen of the dietary restriction (DR) to study its effect on epileptogenesis and neuroprotection in the pilocarpine model of TLE in rats. The effect of IF regimen on the induction of status epilepticus (SE), the duration of latent period, and the frequency, duration, severity and the time of occurrence of Spontaneous Recurrent Seizures (SRS) were investigated. We also studied the effect of IF regimen on hippocampal neurons against the excitotoxic damage of prolonged SE (about 4h) induced by pilocarpine. The animals (Wistar, male, 200-250g) were divided into four main groups: AL-AL (ad libitum diet throughout), AL-IF (PfS) [IF post-first seizure], AL-IF (PSE) [IF post-SE] and IF-IF (IF diet throughout), and two AL and IF control groups. SE was induced by pilocarpine (350mg/kg, i.p.) and with diazepam (6mg/kg, i.p.) injected after 3h, the behavioral signs of SE terminated at about 4h (AL animals, n=29, 260.43+/-8.74min; IF animals, n=19, 224.32+/-20.73min). Behavioral monitoring was carried out by 24h video recording for 3 weeks after the first SRS. Rat brains were then prepared for histological study with Nissl stain and cell counting was done in CA1, CA2 and CA3 regions of the hippocampus. The results show that the animals on IF diet had significantly less SE induction and significantly longer duration of latent period (the period of epileptogenesis) was seen in IF-IF group compared to the AL-AL group. The severity of SRS was significantly more in AL-IF (PfS) compared to the AL-IF (PSE) group. These results indicate that IF diet can make rats resistant to the induction of SE and can prolong the process of epileptogenesis. The results of the histological study show that the number of pyramidal neurons was statistically less in CA1, CA2 and CA3 of the hippocampus in the experimental groups compared to the control groups. However, IF regimen could not protect the hippocampal neurons against the excitotoxic injury caused by a prolonged SE. We conclude that IF regimen can significantly influence various behavioral characteristics of pilocarpine model of TLE. Further studies can elaborate the exact mechanisms as well as its possible role in the treatment of human TLE.

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.

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.

Apolipoprotein E and cholesterol in aging and disease in the brain

Cholesterol can be detrimental or vital, and must be present in the right place at the right time and in the right amount. This is well known in the heart and the vascular system. However, in the CNS cholesterol is still an enigma, although several of its fundamental functions in the brain have been identified. Brain cholesterol has attracted additional attention owing to its close connection to ApoE, a key polymorphic transporter of extracellular cholesterol in humans. Indeed, both cholesterol and ApoE are so critical to fundamental activities of the brain, that the brain regulates their synthesis autonomously. Yet, similar control mechanisms of ApoE and cholesterol homeostasis may exist on either sides of the blood-brain barrier. One indication is that the APOE ε4 allele is associated with hypercholesterolemia and a proatherogenic profile on the vascular side and with increased risk of Alzheimer's disease on the CNS side. In this review, we draw attention to the association between cholesterol and ApoE in the aging and diseased brain, and to the behavior of the ApoE4 protein at the molecular level. The attempt to correlate in vivo and in vitro observations is challenging but crucial for developing future strategies to address ApoE-related aberrations in cholesterol metabolism selectively in the brain.

Age-related changes in glial cells of dopamine midbrain subregions in rhesus monkeys

Aging remains the strongest risk factor for developing Parkinson's disease (PD), and there is selective vulnerability in midbrain dopamine (DA) neuron degeneration in PD. By tracking normal aging-related changes with an emphasis on regional specificity, factors involved in selective vulnerability and resistance to degeneration can be studied. Towards this end, we sought to determine whether age-related changes in microglia and astrocytes in rhesus monkeys are region-specific, suggestive of involvement in regional differences in vulnerability to degeneration that may be relevant to PD pathogenesis. Gliosis in midbrain DA subregions was measured by estimating glia number using unbiased stereology, assessing fluorescence intensity for proteins upregulated during activation, and rating morphology. With normal aging, microglia exhibited increased staining intensity and a shift to more activated morphologies preferentially in the vulnerable substantia nigra-ventral tier (vtSN). Astrocytes did not exhibit age-related changes consistent with an involvement in regional vulnerability in any measure. Our results suggest advancing age is associated with chronic mild inflammation in the vtSN, which may render these DA neurons more vulnerable to degeneration.

Minocycline attenuates lipopolysaccharide (LPS)-induced neuroinflammation, sickness behavior, and anhedonia

Background

Activation of the peripheral innate immune system stimulates the secretion of CNS cytokines that modulate the behavioral symptoms of sickness. Excessive production of cytokines by microglia, however, may cause long-lasting behavioral and cognitive complications. The purpose of this study was to determine if minocycline, an anti-inflammatory agent and purported microglial inhibitor, attenuates lipopolysaccharide (LPS)-induced neuroinflammation, sickness behavior, and anhedonia.

Methods

In the first set of experiments the effect of minocycline pretreatment on LPS-induced microglia activation was assessed in BV-2 microglia cell cultures. In the second study, adult (3–6 m) BALB/c mice received an intraperitoneal (i.p.) injection of vehicle or minocycline (50 mg/kg) for three consecutive days. On the third day, mice were also injected (i.p.) with saline or Escherichia coli LPS (0.33 mg/kg) and behavior (i.e., sickness and anhedonia) and markers of neuroinflammation (i.e., microglia activation and inflammatory cytokines) were determined. In the final study, adult and aged BALB/c mice were treated with the same minocycline and LPS injection regimen and markers of neuroinflammation were determined. All data were analyzed using Statistical Analysis Systems General Linear Model procedures and were subjected to one-, two-, or three-way ANOVA to determine significant main effects and interactions.

Results

Minocycline blocked LPS-stimulated inflammatory cytokine secretion in the BV-2 microglia-derived cell line and reduced LPS-induced Toll-like-receptor-2 (TLR2) surface expression on brain microglia. Moreover, minocycline facilitated the recovery from sickness behavior (i.e., anorexia, weight loss, and social withdrawal) and prevented anhedonia in adult mice challenged with LPS. Furthermore, the minocycline associated recovery from LPS-induced sickness behavior was paralleled by reduced mRNA levels of Interleukin (IL)-1β, IL-6, and indoleamine 2, 3 dioxygenase (IDO) in the cortex and hippocampus. Finally, in aged mice, where exaggerated neuroinflammation was elicited by LPS, minocycline pretreatment was still effective in markedly reducing mRNA levels of IL-1β, TLR2 and IDO in the hippocampus.

Conclusion

These data indicate that minocycline mitigates neuroinflammation in the adult and aged brain and modulates the cytokine-associated changes in motivation and behavior.

Molecular and cellular characterization of the age-related neuroinflammatory processes occurring in normal rat hippocampus: potential relation with the loss of somatostatin GABAergic neurons

Increased neuroinflammatory reaction is frequently observed during normal brain aging. However, a direct link between neuroinflammation and neurodegeneration during aging has not yet been clearly shown. Here, we have characterized the age-related hippocampal inflammatory processes and the potential relation with hippocampal neurodegeneration. The mRNA expression of the pro-inflammatory cytokines IL-1beta and tumor necrosis factor-alpha (TNF-alpha), and the iNOs enzyme was significantly increased in aged hippocampus. Accordingly, numerous activated microglial cells were observed in aged rats. These cells were differentially distributed along the hippocampus, being more frequently located in the hilus and the CA3 area. The mRNA expression of somatostatin, a neuropeptide expressed by some GABAergic interneurons, and the number of somatostatin-immunopositive cells decreased in aged rats. However, the number of hippocampal parvalbumin-containing GABAergic interneurons was preserved. Interestingly, in aged rats, the mRNA expression of somatostatin and IL-1beta was inversely correlated and, the decrease in the number of somatostatin-immunopositive cells was higher in the hilus of dentate gyrus than in the CA1 region. Finally, intraperitoneal chronic lipopolysaccharide (LPS) injection in young animals mimicked the age-related hippocampal inflammation as well as the decrease of somatostatin mRNA expression. Present results strongly support the neuroinflammation as a potential factor involved in the age-related degeneration of somatostatin GABAergic cells.

Exaggerated sickness behavior and brain proinflammatory cytokine expression in aged mice in response to intracerebroventricular lipopolysaccharide

Age-associated changes in glial reactivity may predispose individuals to exacerbated neuroinflammatory cytokine responses that are permissive to cognitive and behavioral complications. The purpose of this study was to determine if aging is associated with an exaggerated sickness response to central innate immune activation. Our results show that intracerebroventricular (i.c.v.) administration of lipopolysaccharide (LPS) caused a heightened proinflammatory cytokine response (IL-1beta, IL-6, and TNFalpha) in the cerebellum 2h post i.c.v. injection in aged mice compared to adults. This amplified inflammatory profile was consistent with a brain region-dependent increase in reactive glial markers (MHC class II, TLR2 and TLR4). Moreover, LPS caused a prolonged sickness behavior response in aged mice that was paralleled by a protracted expression of brain cytokines in the cerebellum and hippocampus. Finally, central LPS injection caused amplified and prolonged IL-6 levels at the periphery of aged mice. Collectively, these data establish that activation of the central innate immune system leads to exacerbated neuroinflammation and prolonged sickness behavior in aged as compared to adult mice.

Gene expression of cyclooxygenase-1 and Ca(2+)-independent phospholipase A(2) is altered in rat hippocampus during normal aging

Brain aging is associated with inflammatory changes. However, data on how the brain arachidonic acid (AA) metabolism is altered as a function of age are limited and discrepant. AA is released from membrane phospholipids by phospholipase A(2) (PLA(2)) and then further metabolized to bioactive prostaglandins and thromboxanes by cyclooxygenases (COX)-1 and -2. We examined the phospholipase A(2) (PLA(2))/COX-mediated AA metabolic pathway in the hippocampus and cerebral cortex of 4-, 12-, 24- and 30-month-old rats. A two-fold increase in brain thromboxane B(2) level in 24 and 30 months was accompanied by increased hippocampal COX-1 mRNA levels at 12, 24, and 30 months. COX-2 mRNA expression was significantly decreased only at 30 months. Hippocampal Ca(2+)-independent iPLA(2) mRNA levels were decreased at 24 and 30 months without any change in Ca(2+)-dependent PLA(2) expression. In the cerebral cortex, mRNA levels of COX and PLA(2) were not significantly changed. The specific changes in the AA cascade observed in the hippocampus may alter phospholipids homeostasis and possibly increase the susceptibility of the aging brain to neuroinflammation.

Ladostigil prevents gliosis, oxidative–nitrative stress and memory deficits induced by intracerebroventricular injection of streptozotocin in rats

Glial activation and oxidative-nitrative stress occur at an early stage in Alzheimer's disease (AD). In a rat model of AD, deficits in cerebral glucose utilization and memory were seen 3-4 weeks after intracerebroventricular (icv) injection of streptozotocin (STZ). This study examined whether icv STZ induced glial activation and oxidative-nitrative stress preceded the memory deficits and whether they could be prevented by ladostigil a novel drug, a cholinesterase and monoamine oxidase inhibitor with neuroprotective activity. One week after STZ injection activated microglia and astrocytes were seen in the cortex, around the cannula penetration area, in the hippocampal CA1 region, corpus callosum, medial and lateral septum. The activated astrocytes showed a significant increase in nitrotyrosine immunoreactivity, a measure of oxidative-nitrative stress. Only 3 weeks later were deficits in episodic (object recognition test) and spatial memory (place recognition) seen in STZ-injected rats. Daily oral administrations of ladostigil (1mg/kg) for 1 week, before and after STZ prevented the glial changes, increase in nitrotyrosine immunoreactivity and memory deficits. Taken together the data support the role of glial activation and oxidative-nitrative stress in discrete brain areas in the aetiology of memory deficits and indicate a potential mechanism for their prevention by drug treatment.

Age-related alterations of Apolipoprotein E and interleukin-1beta in the aging brain

With normal aging, the brain undergoes several alterations including reduced neuronal functioning and alterations in glia homeostasis. An increase in inflammatory signaling has also been reported in some studies of the aging brain, with inflammation potentially mediating age-related changes in the brain. Apolipoprotein E (ApoE) is produced in the brain and has been shown to possess anti-inflammatory properties in a variety of paradigms. In the present study, we correlated age-related alterations in ApoE expression with age-related changes in the cytokine interleukin-1 beta (IL-1beta), in the brain of rats of increasing age. No significant alteration in ApoE mRNA was found in any region examined. A significant increase in IL-1beta mRNA with age was observed only in the cortex. Neither ApoE nor IL-1beta protein expression was significantly altered with age in the brain. A significant linear correlation between ApoE and IL-1beta mRNA was found in the cortex but not in the striatum or hippocampus. No correlation was found between ApoE and IL-1beta protein in any region examined. Taken together, these studies demonstrate that ApoE expression is not altered during normal brain aging, but suggest that there may be a relationship between ApoE and IL-1beta transcription in the cerebral cortex.

Age and Neuroinflammation: A Lifetime of Psychoneuroimmune Consequences

This article reviews the literature indicating that the innate immune cells of the brain become more reactive with age. Although it is unclear how glia reactivity increases, emerging evidence suggests these alterations allow exacerbated neuroinflammation and sickness behavior following peripheral immune activation. This amplified or prolonged exposure to inflammatory cytokines in the brain may impair neuronal plasticity and underlie a heightened neuroinflammatory response in the aged that also may lead to other neurobehavioral impairments such as delirium, depression, and, potentially, the onset of neurologic disease. Therefore pharmacologic strategies to decrease neuroinflammation associated with infection may be important for improving recovery from sickness and reducing neurobehavioral deficits in the elderly.

Microglia in the aging brain

The aging brain is characterized by a demonstrable decrease in weight and volume, particularly after the age of 50. This atrophy, which affects both grey and white matter, is presumed to result from a loss of neurons and myelinated axons. Glial cells, on the other hand, appear to increase in the aging brain, which exhibits greater immunoreactivity with both astrocytic and microglial markers. This review is focused on the morphologic and phenotypic changes that occur in microglial cells with normal aging. Although there is a consistent aging-related upregulation of microglial activation markers in experimental animals and humans that could be interpreted as aging-related neuroinflammation, it is generally difficult to show a direct correlation between ostensible microglial activation and neurodegeneration. This raises questions about whether aging-related microglial activation indeed represents reactive gliosis in the conventional sense. As an alternative, we discuss the possibility that structural and phenotypic changes that occur in microglia are a direct reflection of the aging process on microglia. Thus, microglia cells themselves may be subject to cellular senescence in the sense that they no longer function efficiently. The concept of microglial senescence offers a novel perspective on aging-related neurodegeneration, namely that neurodegeneration could also occur secondary to microglial degeneration.

Cytokine-induced activation of glial cells in the mouse brain is enhanced at an advanced age

Numerous neurological diseases which include neuroinflammatory components exhibit an age-related prevalence. The aging process is characterized by an increase of inflammatory mediators both systemically and in the brain, which may prime glial cells. However, little information is available on age-related changes in the glial response of the healthy aging brain to an inflammatory challenge. This problem was here examined using a mixture of the proinflammatory cytokines interferon-gamma and tumor necrosis factor-alpha, which was injected intracerebroventricularly in young (2-3.5 months), middle-aged (10-11 months) and aged (18-21 months) mice. Vehicle (phosphate-buffered saline) was used as control. After a survival of 1 or 2 days (all age groups) or 4 days (young and middle-aged animals), immunohistochemically labeled astrocytes and microglia were investigated both qualitatively and quantitatively. In all age groups, astrocytes were markedly activated in periventricular as well as in deeper brain regions 2 days following cytokine treatment, whereas microglia activation was already evident at 24 h. Interestingly, cytokine-induced activation of both astrocytes and microglia was significantly more marked in the brain of aged animals, in which it included numerous ameboid microglia, than of younger age groups. Moderate astrocytic activation was also seen in the hippocampal CA1 field of vehicle-treated aged mice. FluoroJade B histochemistry and the terminal deoxynucleotidyl transferase-mediated UTP nick-end labeling technique, performed at 2 days after cytokine administration, did not reveal ongoing cell death phenomena in young or aged animals. This indicated that glial cell changes were not secondary to neuronal death. Altogether, the findings demonstrate for the first time enhanced activation of glial cells in the old brain, compared with young and middle-aged subjects, in response to cytokine exposure. Interestingly, the results also suggest that such enhancement does not develop gradually since youth, but appears characterized by relatively late onset.

mRNA up-regulation of MHC II and pivotal pro-inflammatory genes in normal brain aging

In normal brain aging, CNS resident macrophages exhibit increased expression of major histocompatibility complex (MHC) II expression. However, the transcriptional basis for this observation has not been clarified nor have age-related alterations in pivotal pro-inflammatory genes been characterized. Age-related mRNA alterations in MHC II, MHC II accessory molecules and several pro-inflammatory mediators were measured in older (24 months) and younger (3 months) male F344xBN F1 rats. Real time RT-PCR was utilized to measure steady state mRNA levels in hippocampus. Older as compared to younger animals exhibited increased mRNA levels of MHC II, CD86, CIITA and IFN-gamma. Furthermore, IL-10 and CD200 mRNA, molecules that down-regulate macrophage activation, was decreased in older animals. The present results indicate that normal brain aging is characterized by a shift towards a pro-inflammatory microenvironment in the CNS.

Caloric restriction in C57BL/6J mice mimics therapeutic fasting in humans

Background

Caloric restriction (CR) has long been recognized as a dietary therapy that improves health and increases longevity. Little is known about the persistent effects of CR on plasma biomarkers (glucose, ketone bodies, and lipids) following re-feeding in mice. It is also unclear how these biomarker changes in calorically restricted mice relate to those observed previously in calorically restricted humans.

Results

Three groups of individually housed adult female C57BL/6J (B6) mice (n = 4/group) were fed a standard rodent chow diet either: (1) unrestricted (UR); (2) restricted for three weeks to reduce body weight by approximately 15–20% (R); or (3) restricted for three weeks and then re-fed unrestricted (ad libitum) for an additional three weeks (R-RF). Body weight and food intake were measured throughout the study, while plasma lipids and levels of glucose and ketone bodies (β-hydroxybutyrate) were measured at the termination of the study. Plasma glucose, phosphatidylcholine, cholesterol, and triglycerides were significantly lower in the R mice than in the UR mice. In contrast, plasma fatty acids and β-hydroxybutyrate were significantly higher in the R mice than in the UR mice. CR had no effect on plasma phosphatidylinositol levels. While body weight and plasma lipids of the R-RF mice returned to unrestricted levels upon re-feeding, food intake and glucose levels remained significantly lower than those prior to the initiation of CR.

Conclusion

CR establishes a new homeostatic state in B6 mice that persists for at least three weeks following ad libitum re-feeding. Moreover, the plasma biomarker changes observed in B6 mice during CR mimic those reported in humans on very low calorie diets or during therapeutic fasting.

Influence of caloric restriction on motor behavior, longevity, and brain lipid composition in Sandhoff disease mice

Caloric restriction (CR), which improves health and increases longevity, was studied as a therapy in a hexosaminidase beta knockout mouse model of Sandhoff disease (SD), an incurable neurodegenerative disease involving accumulation of brain ganglioside GM2 and asialo-GM2 (GA2). Adult mice were fed a rodent chow diet either ad libitum (AL) or restricted to reduce body weight by 15-18% (CR). Although GM2 and GA2 were elevated, no significant differences were seen between the Hexb-/- and the Hexb+/- mice for most brain phospholipids and cholesterol. Cerebrosides and sulfatides were reduced in the Hexb-/- mice. In addition, rotorod performance was significantly worse in the Hexb-/- mice than in the Hexb+/- mice. CR, which decreased circulating glucose and elevated ketone bodies, significantly improved rotorod performance and extended longevity in the Hexb-/- mice but had no significant effect on brain lipid composition or on cytoplasmic neuronal vacuoles. The expression of CD68 and F4/80 was significantly less in the CR-fed than in the AL-fed Hexb-/- mice. We suggest that the CR delays disease progression in SD and possibly in other ganglioside storage diseases through anti-inflammatory mechanisms.

Macrosialin increases during normal brain aging are attenuated by caloric restriction

During normal aging, microglia develop an activated phenotype characterized by morphologic changes and induction of CD11b, MHC II, and other inflammatory markers. We show that macrosialin (CD68), a macrophage-specific protein, is increased by aging in selected brain regions of male C57BL/6NNia mice. In corpus callosum and striatum, macrosialin mRNA and protein increased >or=50% (24 months versus 4 months); hippocampus and cerebellum were unchanged. Caloric restriction (CR) attenuated these age-related increases. Since CR attenuates age-related increases in oxidative damage and inflammation, we examined whether oxidized lipoproteins and inflammatory processes regulate macrosialin using murine BV-2 microglial cells as a model. Oxidized low-density lipoproteins (oxLDL) induced macrosialin protein by 50%. Moreover, macrosialin was induced in response to lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma) which activates inflammatory pathways in BV-2 cells. Thus, the previously documented increase in oxidized lipoproteins, inflammation, and microglial activation during normal aging may contribute to the age-related increase in macrosialin expression.

Effect of aging on the microglial response to peripheral nerve injury

Microglial morphology and immunophenotype have been studied extensively in aging-related neurodegenerative diseases, but to a lesser extent in the normally aged CNS, and little is known about how aging affects the ability of microglia to respond to neuronal injury. The goal of the current study was to determine if aging affects the ability of microglia to divide during the early response to facial nerve axotomy. In addition, we investigated the incidence of microglial cell death during later post-axotomy time points to determine if aging had an effect on microglial turnover. We employed DNA labeling with 3H-thymidine, TUNEL and lectin histochemistry after facial nerve axotomy in young (3 months), middle-aged (15 months), and old (30 months) Fisher344-Brown Norway hybrid rats. Proliferation of microglia in old rats remained significantly higher than in young rats 4 days after injury, suggesting that regulation of microglial proliferation changes with aging. There was no aging-related difference in microglial TUNEL staining at 7, 14 or 21 days post-axotomy. Lectin histochemistry in the unoperated facial nucleus revealed aging-related morphological changes in resting microglia, including hypertrophy of the cytoplasm with dense perinuclear staining. Aging-related differences in activated microglia on the lesioned side were more subtle, although many activated microglia of aged animals continued to exhibit dense perinuclear lectin reactivity. We propose that aging-related changes in morphology in conjunction with a less regulated proliferative response in the aged facial nucleus may be a reflection of microglial senescence.

Protective effects of melatonin against ethanol-induced reactive gliosis in hippocampus and cortex of young and aged rats

Evidence has been accumulated indicating that chronic ethanol consumption leads to direct or indirect changes in the viability of central nervous system cells. The effects of aging and chronic ethanol consumption on glial markers [glial fibrillary acidic protein (GFAP) and S100B] and oxidant and antioxidant status of rats were studied. Furthermore, protective effects of melatonin against aging and alcohol consumption were also assayed. Chronic ethanol administration to young and aged rats produced an increase in lipid peroxidation, and a decline in glutathione (GSH) levels, which was significantly reversed by the co-administration of melatonin. Lipid peroxidation status was markedly affected in aged rats treated with alcohol compared to the young rats. An age-related increase in GFAP and S100B levels were found in the cortex and hippocampus. Long-term alcohol exposure resulted in distinct elevation in GFAP content in young rats (P < 0.01) while there was less increase in the cortex of aged rats (P < 0.05). In old rats, hippocampal GFAP levels were not significantly changed by alcohol treatment (P > 0.05). Co-administration of melatonin with alcohol significantly reduced GFAP contents both in the hippocampus (P < 0.01) and cortex (P < 0.001) of aged rats. No significant effects of alcohol treatment were found on the levels of neuron-specific enolase (NSE) in aged rats. This finding suggests that melatonin exerts its protective effect on injured nervous tissues by scavenging free radicals and stabilizing glial activity against the damaging effects of ethanol and aging. Furthermore, this work suggests that the signal to initiate gliosis is mediated, at least indirectly, by free radical formation.

Caloric restriction attenuates Aβ-deposition in Alzheimer transgenic models

Dietary influences on Alzheimer disease (AD) are gaining recognition. Because many aging processes are attenuated in laboratory mammals by caloric restriction (CR), we examined the effects of short-term CR in two AD-transgenic mice, APP(swe/ind) (J20) and APP(swe) + PS1(M146L) (APP + PS1). CR substantially decreased the accumulation of Abeta-plaques in both lines: by 40% in APP(swe/ind) (CR, 6 weeks), and by 55% in APP + PS1 (CR, 14 weeks). CR also decreased astrocytic activation (GFAP immunoreactivity). These influences of CR on AD-transgenic mice are consistent with epidemiological reports that show that high caloric diets associate with the risk of AD, and suggest that dietary interventions in adult life might slow disease progression.

Exaggerated neuroinflammation and sickness behavior in aged mice following activation of the peripheral innate immune system

Acute cognitive impairment (i.e., delirium) is common in elderly emergency department patients and frequently results from infections that are unrelated to the central nervous system. Since activation of the peripheral innate immune system induces brain microglia to produce inflammatory cytokines that are responsible for behavioral deficits, we investigated if aging exacerbated neuroinflammation and sickness behavior after peripheral injection of lipopolysaccharide (LPS). Microarray analysis revealed a transcriptional profile indicating the presence of primed or activated microglia and increased inflammation in the aged brain. Furthermore, aged mice had a unique gene expression profile in the brain after an intraperitoneal injection of LPS, and the LPS-induced elevation in the brain inflammatory cytokines and oxidative stress was both exaggerated and prolonged compared with adults. Aged mice were anorectic longer and lost more weight than adults after peripheral LPS administration. Moreover, reductions in both locomotor and social behavior remained 24 h later in aged mice, when adults had fully recovered, and the exaggerated neuroinflammatory response in aged mice was not reliably paralleled by increased circulating cytokines in the periphery. Taken together, these data establish that activation of the peripheral innate immune system leads to exacerbated neuroinflammation in the aged as compared with adult mice. This dysregulated link between the peripheral and central innate immune system is likely to be involved in the severe behavioral deficits that frequently occur in older adults with systemic infections.