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

Reversible age impairments in neurite outgrowth by manipulations of astrocytic GFAP

Aging is associated with neuron atrophy and impaired sprouting after lesions. In contrast during normal aging without neurodegenerative diseases, astrocytes display increasing activation, with progressive increases of glial fibrillary acidic protein (GFAP) beginning before midlife. Because many neuronal functions depend on astrocytic support, we developed a heterochronic co-culture system to study influences of aging astrocytes on neurons. Neurite outgrowth by embryonic neurons (E18) was markedly less when co-cultured with confluent astrocytes derived from old (24 mo) versus young (3 mo) cortex. These impairments were reversible. Diminishing the GFAP levels of old astrocytes by RNAi restored neurite outgrowth, whereas overexpression of GFAP in young astrocytes modeled these effects of aging by reducing neurite outgrowth. Quantitative relationships were found such that neurites were co-localized with high intensity laminin, which both varied inversely with GFAP. These results implicate increased astrocytic GFAP expression as a proximal cause of neuron atrophy during normal aging.

Growth hormone prevents neuronal loss in the aged rat hippocampus

Decline of growth hormone (GH) with aging is associated to memory and cognitive alterations. In this study, the number of neurons in the hilus of the dentate gyrus has been assessed in male and female Wistar rats at 3, 6, 12, 14, 18, 22 and 24 months of age, using the optical fractionator method. Male rats had more neurons than females at all the ages studied. Significant neuronal loss was observed in both sexes between 22 and 24 months of age. In a second experiment, 22 month-old male and female rats were treated for 10 weeks with 2 mg/kg/day of GH or saline. At 24 months of age, animals treated with GH had more neurons in the hilus than animals treated with saline. These findings indicate that GH is neuroprotective in old animals and that its administration may ameliorate neuronal alterations associated to aging.

Aging, stress and the hippocampus

Functional loss often occurs in many body systems (e.g., endocrine, cognitive, motor) with the passage of years, but there is great individual variation in the degree of compromise shown. The current focus on brain aging will continue because demographic trends indicate that the average lifespan will show a continued increase. There is increasing emphasis on understanding how aging contributes to a decline in brain functions, cognition being a prime example. This is due in part to the fact that dementias and other losses in brain function that sometimes accompany aging cause an obvious decline in the quality of life and these deficits are of more concern as the number of elderly increase. Stress also is a ubiquitous aspect of life and there is now a greater interest in understanding the role of stress and the stress response in brain aging. The key role of the hippocampus and its related brain structures in cognition, as well as in the feedback control of the response to stress, have made this brain area a logical focus of investigation for those interested in the impact of stress on brain aging. Here, we describe how the hippocampus changes with age and we examine the idea that age-related changes in the secretion patterns of the hypothalamic-pituitary adrenal (HPA) axis can contribute to aging of this structure. We also examine the proposal that stress, perhaps due to compromised HPA axis function, can contribute to hippocampal aging through exposure to excessive levels of glucocorticoids. The aging hippocampus does not appear to suffer a generalized loss of cells or synapses, although atrophy of the structure may occur in humans. Thus, age-related cognitive impairments are likely related to other neurobiological alterations that could include changes in the signaling, information encoding, plasticity, electrophysiological or neurochemical properties of neurons or glia. Although excessive levels of glucocorticoids are able to interfere with cognition, as well as hippocampal neuronal integrity, and aging is sometimes accompanied by an increase in these steroids because of inadequate feedback control of the HPA axis, none of these are a foregone consequence of aging. The general preservation of cells and the plastic potential of the hippocampus provide a focus for the development of pharmacological, nutritive or lifestyle strategies to combat age-related declines in the hippocampus as well as other brain areas.

Developmental origins of aging in brain and blood vessels: an overview

Emerging evidence suggests a remarkable convergence of inflammatory mechanisms in the etiology of cardiovascular disease and Alzheimer disease. A broad set of NSAIDs and statins used to reduce the risk of vascular occlusion and to slow atherogensis may also be protective for Alzheimer disease. Elevated blood levels of C-reactive protein are risk factors for cardiovascular disease and possibly for Alzheimer disease. Monocyte-lineage cells are also fundamental to both conditions: in blood vessels, macrophages are important to atherogenesis for the accumulation of lipids (foam cells), whereas brain microglia show activation during aging and direct involvement in amyloid metabolism in the senile plaque. Genetic influences are recognized through the apoE4 allele, which is associated with hypercholesterolemia and is a risk factor in vascular events and Alzheimer disease, and is recognized for its proinflammatory profile. ApoE4 also accelerates Alzheimer disease pathogenesis in Down's syndrome and many other chronic neurodegenerative conditions, as is well-supported by animal models. Inflammatory changes are present at the earliest stages of vascular disease and Down's syndrome in human fetuses, and are also prominent early in Alzheimer disease. These findings give a basis for considering inflammatory processes early in life which can lead to fully fired pathogenesis of cardiovascular disease and possibly for Alzheimer disease.

Progressive changes in regulation of apolipoproteins E and J in glial cultures during postnatal development and aging

Apolipoprotein (Apo) E and ApoJ are lipid- and cholesterol-carriers in the central nervous system and are implicated in age-related neurodegenerative diseases. The primary source of secreted ApoE and ApoJ (clusterin) in the brain is glia. Regulation of these apolipoproteins in mixed glial cultures from rat cerebral cortex differed most strongly between neonatal- and adult-derived glia. Basal secretion of ApoJ was two-fold greater in neonatal than adult glia. Responses to cytokines also differed by donor age. In adult glia, IL-6 increased ApoE secretion, but slightly decreased ApoJ. Both IL-1 beta and TNFalpha treatments increased ApoJ secretion from adult glia, with little effect on ApoE. In contrast to adult glia, neonatal ApoJ secretion did not respond to IL-1 beta, IL-6, or TNFalpha, and ApoE secretion from neonatal glia was slightly increased by IL-6. These differences may contribute to age-related neuroinflammatory processes, and are pertinent to the general use of neonatal-derived primary glia in models for neurodegenerative disease.

Age- and sex-dependent development of adrenocortical hyperactivity in a transgenic mouse model of Alzheimer's disease

In this study, we investigated mice of the TgCRND8 line, an APP transgenic mouse model of Alzheimer's disease (AD), with respect to behavioral, endocrinological, and neuropathological parameters. Our results show that transgenic and wild-type mice did not differ in their general health status, exploratory and anxiety related behavior as well as in the activity of their sympathetic-adrenomedullary system. Significant differences, however, were found regarding body weight, amyloid plaque formation, and the activity of the hypothalamic-pituitary-adrenocortical (HPA) axis. Continuous monitoring of glucocorticoid (GC) concentrations over a period of 120 days, utilizing a noninvasive technique to measure corticosterone metabolites in fecal samples, revealed that transgenic animals showed adrenocortical hyperactivity, starting very early in males (from day 30) and later in females (around day 90). It is hypothesized that these changes in the activity of the HPA axis are linked to amyloid-beta associated pathological alterations in the hippocampus, causing degenerations in the negative feedback regulation of the HPA axis leading to hypersecretion of GC. Thus, the development of adrenocortical hyperactivity might be a key-element in the understanding of AD.

Neuronal susceptibility to damage: comparison of the retinas of young, old and old/caloric restricted rats before and after transient ischemia

Compared to young rats, old age increases susceptibility and caloric restriction decreases susceptibility for the loss of retinal ganglion cells and displaced amacrine cells following retinal ischemia/reperfusion. In retinas of old animals before ischemia, reactive gliosis, including activation of Muller cells, microglia and astrocytes, is increased compared to retinas from young and old/caloric restricted animals. Post-ischemia, the existing reactive gliosis in retinas of old animals is not neuroprotective and the reactive gliosis is even further increased in old animals compared to young or old/caloric restricted animals. In retinas from old/caloric restricted animals, inducible heat shock protein-70 and brain-derived neurotrophic factor increased more markedly after ischemia/reperfusion compared to retinas from young and old animals. Thus, compared to retinas in young animals, neurons of old animals may be more susceptible to cell death by secondary glial mechanisms after retinal ischemia/reperfusion. Caloric restriction in old animals is neuroprotective against damage in the retina following ischemia, perhaps by suppressing glial activity and by the neuroprotective effects of inducible heat shock protein-70 and brain-derived neurotrophic factor.

Quantitative age-related changes in dorsal lateral geniculate nucleus relay neurons of the rat

An ultrastructural and quantitative study of the age-related changes occurring in the relay neurons of the dorsal lateral geniculate nucleus (dLGN) was carried out using male Wistar rats aged 3, 18, 24, and 28 months. Morphometric techniques were used to obtain data regarding cellular activity including soma, nuclear, and nucleolar size. Volume fractions for rough endoplasmic reticulum (RER), mitochondria, and lipofuscin, as well as numbers and sizes of mitochondria and dense bodies (DB) was also calculated. Among the few alterations found in the perikaryon, we can highlight the redistribution and fragmentation of RER and an increase and progressive aggregation of lipofuscin. Quantitative data show a significant decrease in the volume of the soma (-42.77%) and the nucleus (-33.66%), and in the volume fraction of the RER (-18.81%) and mitochondria (-10.16%). A significant increase in lipofuscin (+213.29%), and variations in size and number of mitochondria and dense bodies were also found. Some histophysiological considerations about the findings are discussed. The findings lead to the conclusion that a relative degree of morphological stability is exhibited by relay neurons, although the quantitative data show evident intracellular changes, especially from 24 to 28 months. These changes suggest that accompanying physiological alterations may occur, with putative effects on visual function during ageing.

The cholesterol-lowering drug probucol increases apolipoprotein E production in the hippocampus of aged rats: implications for Alzheimer's disease

Several recent epidemiological studies have proposed that cholesterol-lowering drug Statin may provide protection against Alzheimer's disease (AD). Probucol is a non-Statin cholesterol-lowering drug and a potent inducer of apolipoprotein E (apoE) production in peripheral circulation. A recent clinical study using Probucol in elderly AD subjects revealed a concomitant stabilisation of cognitive symptoms and significant increases in apoE levels in the cerebral spinal fluid in these patients. To gain insight into the mechanisms underlying these effects, we treated a cohort of aged male rats (26-month-old) with oral dose of Probucol for 30 days. Specifically, we examined the effects of Probucol on apoE production and its receptors (low density lipoprotein receptor [LDLr] and low density lipoprotein receptor-related protein [LRP]), astroglial marker of cell damage (glial fibrillary acidic protein [GFAP]), markers of neuronal synaptic plasticity and integrity (synaptosomal associated protein of 25 kDa [SNAP-25] and synaptophysin) as well as cholesterol biosynthesis (3-hydroxy-3-methylglutaryl coenzyme A reductase [HMGCoAr]) in the hippocampus. We report that Probucol induces the production of apoE and one of its main receptors, LRP, increases HMGCoAr (rate-limiting enzyme in cholesterol synthesis), substantially attenuates age-related increases in glial activation, and induces production of synaptic marker SNAP-25, a molecule commonly associated with synaptogenesis and dendritic remodeling. These findings suggest that Probucol could promote neural and synaptic plasticity to counteract the synaptic deterioration associated with brain aging through an apoE/LRP-mediated system. Consistent with the beneficial effects of other cholesterol-lowering drugs such as the Statin, Probucol could also offers additional benefits based on apoE neurobiology.

Aging potentiates Abeta-induced depletion of SNAP-25 in mouse hippocampus

Previously we showed that in Tg2576 mouse hippocampus, synaptosomal-associated protein 25 (SNAP-25) immunoreactivity (IR) is greatly reduced and intracerebroventricular injection of anti-Abeta reverses this depletion. 3- and 24-month-old wild-type mice received juxta-amygdala injection of Abeta42 and hippocampal sections were analyzed for glial fibrillary acidic protein (GFAP)- and SNAP-25-IR at intervals after injections. In young mice, SNAP-IR declined >95% at 1 week in DG-Smi and remained low until 8 weeks, while decreasing in SR, SL and hilum by 8-27% at 1 week and returning to baseline by 2 weeks. There was no change in DG-SMm. In old mice, DG-Smi was specifically depleted in SNAP-IR by >95% even before injection. At 2 weeks, SNAP-IR had declined in all layers by 30-39% of baseline values and by 8 weeks had returned to control values, except the DG-SMm which showed only a 10% reduction at 2 weeks. Baseline GFAP-IR was 10-fold higher in old than in young mice in the fimbria/IC but not appreciably changed in hippocampus. In young mice, the injections of Abeta caused 20-fold increases in GFAP-IR in the fimbria/IC and 2-fold increases in the hippocampal neuropil at 1 week, all of which values returned to baseline by 8 weeks. In old mice, Abeta injections caused relatively much larger increases in GFAP-IR in the hippocampal neuropil than in the fimbria/IC and the GFAP-IR remained greatly increased at 8 weeks.

CONCLUSIONS

the Abeta effect on presynaptic SNAP-25 depletion is increased with age. DG-SMi shows the most severe changes and therefore may represent the most critical site in hippocampus for Abeta neurotoxicity.

Peripherin is not a contributing factor to motor neuron disease in a mouse model of amyotrophic lateral sclerosis caused by mutant superoxide dismutase

Peripherin is a type III intermediate filament protein detected in axonal spheroids associated with amyotrophic lateral sclerosis (ALS). The overexpression of peripherin induces degeneration of spinal motor neurons during aging in transgenic mice and in cultured neuronal cells derived from peripherin transgenic embryos. Here, we investigated whether peripherin is a contributor of pathogenesis in mice overexpressing a mutant superoxide dismutase 1 (SOD1(G37R)) gene linked to familial ALS. This was done by the generation and analysis of SOD1(G37R) mice that either overexpress a peripherin transgene (G37R;TgPer mice) or lack the endogenous peripherin gene (G37R;Per-/- mice). Surprisingly, upregulation or suppression of peripherin expression had no effects on disease onset, mortality, and loss of motor neurons in SOD1(G37R) mice. These results provide compelling evidence that peripherin is not a key contributor of motor neuron degeneration associated with toxicity of mutant SOD1.

Neurons, glia, and plasticity in normal brain aging

Early manifestations of brain aging have received much less attention than the drastic degeneration of AD and MID. During nonpathological changes of normal aging, brain systems differ in the involvement of neuron loss. Spatial learning can become impaired without evidence for neuron loss, whereas eye-blink conditioning deficits are well correlated with Purkinje neuron loss. Glial activation, in particular the increased expression of glial fibrillary acidic protein (GFAP), may be a factor in impaired synaptic plasticity. Lastly, it is discussed how developmental variations in the numbers of Purkinje cells and ovarian oocytes can be factors in outcomes of aging that are not under strict genetic control.

Genetic or pharmacological iron chelation prevents MPTP-induced neurotoxicity in vivo: a novel therapy for Parkinson's disease

Studies on postmortem brains from Parkinson's patients reveal elevated iron in the substantia nigra (SN). Selective cell death in this brain region is associated with oxidative stress, which may be exacerbated by the presence of excess iron. Whether iron plays a causative role in cell death, however, is controversial. Here, we explore the effects of iron chelation via either transgenic expression of the iron binding protein ferritin or oral administration of the bioavailable metal chelator clioquinol (CQ) on susceptibility to the Parkinson's-inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrapyridine (MPTP). Reduction in reactive iron by either genetic or pharmacological means was found to be well tolerated in animals in our studies and to result in protection against the toxin, suggesting that iron chelation may be an effective therapy for prevention and treatment of the disease.

Cytokines and cognition--the case for a head-to-toe inflammatory paradigm

The brain is not only immunologically active of its own accord, but also has complex peripheral immune interactions. Given the central role of cytokines in neuroimmmunoendocrine processes, it is hypothesized that these molecules influence cognition via diverse mechanisms. Peripheral cytokines penetrate the blood-brain barrier directly via active transport mechanisms or indirectly via vagal nerve stimulation. Peripheral administration of certain cytokines as biological response modifiers produces adverse cognitive effects in animals and humans. There is abundant evidence that inflammatory mechanisms within the central nervous system (CNS) contribute to cognitive impairment via cytokine-mediated interactions between neurons and glial cells. Cytokines mediate cellular mechanisms subserving cognition (e.g., cholinergic and dopaminergic pathways) and can modulate neuronal and glial cell function to facilitate neuronal regeneration or neurodegeneration. As such, there is a growing appreciation of the role of cytokine-mediated inflammatory processes in neurodegenerative diseases such as Alzheimer's disease and vascular dementia. Consistent with their involvement as mediators of bidirectional communication between the CNS and the peripheral immune system, cytokines play a key role in the hypothalamic-pituitary-adrenal axis activation seen in stress and depression. In addition, complex cognitive systems such as those that underlie religious beliefs, can modulate the effects of stress on the immune system. Indirect means by which peripheral or central cytokine dysregulation could affect cognition include impaired sleep regulation, micronutrient deficiency induced by appetite suppression, and an array of endocrine interactions. Given the multiple levels at which cytokines are capable of influencing cognition it is plausible that peripheral cytokine dysregulation with advancing age interacts with cognitive aging.

Inflammation in neurodegenerative disease--a double-edged sword

Inflammation is a defense reaction against diverse insults, designed to remove noxious agents and to inhibit their detrimental effects. It consists of a dazzling array of molecular and cellular mechanisms and an intricate network of controls to keep them in check. In neurodegenerative diseases, inflammation may be triggered by the accumulation of proteins with abnormal conformations or by signals emanating from injured neurons. Given the multiple functions of many inflammatory factors, it has been difficult to pinpoint their roles in specific (patho)physiological situations. Studies of genetically modified mice and of molecular pathways in activated glia are beginning to shed light on this issue. Altered expression of different inflammatory factors can either promote or counteract neurodegenerative processes. Since many inflammatory responses are beneficial, directing and instructing the inflammatory machinery may be a better therapeutic objective than suppressing it.

Modification of brain aging and neurodegenerative disorders by genes, diet, and behavior

Multiple molecular, cellular, structural, and functional changes occur in the brain during aging. Neural cells may respond to these changes adaptively, or they may succumb to neurodegenerative cascades that result in disorders such as Alzheimer's and Parkinson's diseases. Multiple mechanisms are employed to maintain the integrity of nerve cell circuits and to facilitate responses to environmental demands and promote recovery of function after injury. The mechanisms include production of neurotrophic factors and cytokines, expression of various cell survival-promoting proteins (e.g., protein chaperones, antioxidant enzymes, Bcl-2 and inhibitor of apoptosis proteins), preservation of genomic integrity by telomerase and DNA repair proteins, and mobilization of neural stem cells to replace damaged neurons and glia. The aging process challenges such neuroprotective and neurorestorative mechanisms. Genetic and environmental factors superimposed upon the aging process can determine whether brain aging is successful or unsuccessful. Mutations in genes that cause inherited forms of Alzheimer's disease (amyloid precursor protein and presenilins), Parkinson's disease (alpha-synuclein and Parkin), and trinucleotide repeat disorders (huntingtin, androgen receptor, ataxin, and others) overwhelm endogenous neuroprotective mechanisms; other genes, such as those encoding apolipoprotein E(4), have more subtle effects on brain aging. On the other hand, neuroprotective mechanisms can be bolstered by dietary (caloric restriction and folate and antioxidant supplementation) and behavioral (intellectual and physical activities) modifications. At the cellular and molecular levels, successful brain aging can be facilitated by activating a hormesis response in which neurons increase production of neurotrophic factors and stress proteins. Neural stem cells that reside in the adult brain are also responsive to environmental demands and appear capable of replacing lost or dysfunctional neurons and glial cells, perhaps even in the aging brain. The recent application of modern methods of molecular and cellular biology to the problem of brain aging is revealing a remarkable capacity within brain cells for adaptation to aging and resistance to disease.

Disruption of astroglial interlaminar processes in Alzheimer's disease

A palisade of long, interlaminar astroglial processes in supragranular layers of the cerebral cortex is characteristic of adult individuals of anthropoid species. In the present study, this distinctive cytoarchitectonic feature was analyzed in tissue deriving from the neocortex of cases affected by Alzheimer's disease (n=14) and age-matched control cases (n=10). Samples of different cortical areas, and in particular prefrontal, temporal and striate fields, were analyzed. Astroglia was labeled by glial fibrillary acidic protein immunoreactivity, that allowed a clear distinction between the classical, stellate intralaminar astroglia and the interlaminar glial processes. The occurrence and relative density of neuritic plaques were ascertained in the same specimens with Bielchowsky staining. In most cortical regions of cases diagnosed as severe Alzheimer's disease by the donor institutions, interlaminar astroglia was found to be markedly altered or absent, and replaced by hypertrophic intralaminar astrocytes. Cases diagnosed as milder or uncertain Alzheimer's disease showed a less consistent involvement of the interlaminar glial palisade. Alterations of the interlaminar palisade in the cortex affected by Alzheimer's disease did not strictly correlate with the density of neuritic plaques in the examined specimens. The findings indicate that loss/severe disruption of the interlaminar palisade of astroglial processes is part of the array of neuropathological changes occurring in the cerebral cortex during Alzheimer's disease. In addition, our data indicate that different types of neocortical astrocytes (namely intralaminar and interlaminar astrocytes) respond differently to the pathobiology of Alzheimer's disease in the neocortex, inasmuch as interlaminar processes tend to disappear while intralaminar processes become reactive.

Effects of age on the glial cells in the rhesus monkey optic nerve

The optic nerve is a circumscribed white matter tract consisting of myelinated nerve fibers and neuroglial cells. Previous work has shown that during normal aging in the rhesus monkey, many optic nerves lose some of their nerve fibers, and in all old optic nerves there are both myelin abnormalities and degenerating nerve fibers. The present study assesses how the neuroglial cell population of the optic nerve is affected by age. To address this question, optic nerves from young (4-10 years) and old (27-33 years) rhesus monkeys were examined by using both light and electron microscopy. It was found that with age the astrocytes, oligodendrocytes, and microglia all develop characteristic cytoplasmic inclusions. The astrocytes hypertrophy and fill space vacated by degenerated nerve fibers, and they often develop abundant glial filaments in their processes. Oligodendrocytes and microglial cells both become more numerous with age, and microglial cells often become engorged with phagocytosed debris. Some of the debris can be recognized as degenerating myelin, and in general, the greater the loss of nerve fibers, the more active the microglial cells become.

The genetics of aging

The genetic analysis of life span has only begun in mammals, invertebrates, such as Caenorhabditis elegans and Drosophila, and yeast. Even at this primitive stage of the genetic analysis of aging, the physiological observations that rate of metabolism is intimately tied to life span is supported. In many examples from mice to worms to flies to yeast, genetic variants that affect life span also modify metabolism. Insulin signaling regulates life span coordinately with reproduction, metabolism, and free radical protective gene regulation in C. elegans. This may be related to the findings that caloric restriction also regulates mammalian aging, perhaps via the modulation of insulin-like signaling pathways. The nervous system has been implicated as a key tissue where insulin-like signaling and free radical protective pathways regulate life span in C. elegans and Drosophila. Genes that determine the life span could act in neuroendocrine cells in diverse animals. The involvement of insulin-like hormones suggests that the plasticity in life spans evident in animal phylogeny may be due to variation in the timing of release of hormones that control vitality and mortality as well as variation in the response to those hormones. Pedigree analysis of human aging may reveal variations in the orthologs of the insulin pathway genes and coupled pathways that regulate invertebrate aging. Thus, genetic approaches may identify a set of circuits that was established in ancestral metazoans to regulate their longevity.

Gene expression profiling of aging using DNA microarrays

We have previously employed high density oligonucleotide arrays representing thousands of genes to determine the gene expression profile of the aging process in skeletal muscle (gastrocnemius) and brain (cerebellum and neocortex) of male C57BL/6 mice. Specific gene expression profiles are associated with the aging process of individual organs, and caloric restriction can prevent or retard the establishment of these gene expression alterations. The use of DNA microarrays may provide a new tool to measure biological age on a tissue-specific basis and to evaluate at the molecular level the efficacy of interventions designed to retard the aging process.

Molecular mechanisms of brain aging and neurodegenerative disorders: lessons from dietary restriction

The application of modern molecular and cell biology technologies to studies of the neurobiology of aging provides a window on the molecular substrates of successful brain aging and neurodegenerative disorders. Aging is associated with increased oxidative stress, disturbances in energy metabolism and inflammation-like processes. Dietary restriction (DR) can extend lifespan and might increase the resistance of the nervous system to age-related neurodegenerative disorders. The neuroprotective effect of DR involves a preconditioning response in which the production of neurotrophic factors and protein chaperones is increased resulting in protection against oxyradical production, stabilization of cellular calcium homeostasis, and inhibition of apoptosis. DR might also enhance neurogenesis, synaptic plasticity and self-repair mechanisms.

Apoptotic death of neurons exhibiting peripherin aggregates is mediated by the proinflammatory cytokine tumor necrosis factor-alpha

Peripherin, a neuronal intermediate filament protein associated with axonal spheroids in amyotrophic lateral sclerosis (ALS), induces the selective degeneration of motor neurons when overexpressed in transgenic mice. To further clarify the selectivity and mechanism of peripherin-induced neuronal death, we analyzed the effects of peripherin overexpression in primary neuronal cultures. Peripherin overexpression led to the formation of cytoplasmic protein aggregates and caused the death not only of motor neurons, but also of dorsal root ganglion (DRG) neurons that were cultured from dissociated spinal cords of peripherin transgenic embryos. Apoptosis of DRG neurons containing peripherin aggregates was dependent on the proinflammatory central nervous system environment of spinal cultures, rich in activated microglia, and required TNF-alpha. This synergistic proapoptotic effect may contribute to neuronal selectivity in ALS.

Stressor specificity of central neuroendocrine responses: implications for stress-related disorders

Despite the fact that many research articles have been written about stress and stress-related diseases, no scientifically accepted definition of stress exists. Selye introduced and popularized stress as a medical and scientific idea. He did not deny the existence of stressor-specific response patterns; however, he emphasized that such responses did not constitute stress, only the shared nonspecific component. In this review we focus mainly on the similarities and differences between the neuroendocrine responses (especially the sympathoadrenal and the sympathoneuronal systems and the hypothalamo-pituitary-adrenocortical axis) among various stressors and a strategy for testing Selye's doctrine of nonspecificity. In our experiments, we used five different stressors: immobilization, hemorrhage, cold exposure, pain, or hypoglycemia. With the exception of immobilization stress, these stressors also differed in their intensities. Our results showed marked heterogeneity of neuroendocrine responses to various stressors and that each stressor has a neurochemical "signature." By examining changes of Fos immunoreactivity in various brain regions upon exposure to different stressors, we also attempted to map central stressor-specific neuroendocrine pathways. We believe the existence of stressor-specific pathways and circuits is a clear step forward in the study of the pathogenesis of stress-related disorders and their proper treatment. Finally, we define stress as a state of threatened homeostasis (physical or perceived treat to homeostasis). During stress, an adaptive compensatory specific response of the organism is activated to sustain homeostasis. The adaptive response reflects the activation of specific central circuits and is genetically and constitutionally programmed and constantly modulated by environmental factors.

Dose-dependent decrease in glial fibrillary acidic protein-immunoreactivity in rat cerebellum after lifelong ethanol consumption

The effects of aging and lifelong ethanol consumption on astrocytic morphology and glial fibrillary acidic protein-immunoreactivity (GFAP-IR) in the cerebellar vermis obtained from ethanol-preferring Alko, Alcohol (AA) rats were analyzed by using computer-assisted image analysis. The ethanol-consuming animals (both male and female) were given ethanol (10%-12%, vol./vol.) as the only available fluid for 21 months (3-24 months), whereas the young (3 months) and the old (24 months) controls received water. In the male rats, but not in the female rats, an age-related decrease in GFAP-IR was found in folia II, VII, and X of the molecular layer, and in turn, an age-related increase was found in folium X of the granular layer, indicating opposite changes in GFAP-IR for male rats due to aging in adjacent brain regions. In the female rats, 21 months of daily average ethanol consumption of 6.6 g/kg resulted in decreased GFAP-IR in folium VII of the molecular layer, and the decrease in cerebellar GFAP-IR correlated with the average daily ethanol intake (r=-.886, P=.019) when folia II, IV, VII, and X were analyzed together. No effect of ethanol on GFAP-IR was detected in the granular layer or in the central white matter of the female rats. There was no change in GFAP-IR in any of the three cerebellar layers of the male rats with average daily ethanol consumption of 3.2 g/kg. These results indicate that the Bergmann glial fibers are the GFAP-expressing structures of the cerebellum most sensitive to moderate-to-heavy chronic ethanol exposure and that this effect is dose dependent.

Glial fibrillary acidic protein immunoreactivity in the prefrontal cortex distinguishes younger from older adults in major depressive disorder

BACKGROUND

Recent postmortem studies in major depressive disorder (MDD) provide evidence for a reduction in the packing density and number of glial cells in different regions of the prefrontal cortex; however, the specific types of glia involved in those morphologic changes are unknown.

METHODS

The territory occupied by the astroglial marker glial fibrillary acidic protein (GFAP) was measured as an areal fraction in cortical layers III, IV, and V in sections from the dorsolateral prefrontal cortex (dlPFC) of MDD and control subjects. In addition, the packing density of GFAP-immunoreactive somata was measured by a direct three-dimensional cell counting method.

RESULTS

The mean areal fraction and packing density of GFAP-immunoreactive astrocytes in the dlPFC of MDD subjects were not significantly different from those in control subjects; however, in MDD there was a significant strong positive correlation between age and GFAP immunoreactivity. When the MDD group was divided into younger (30-45 years old) and older (46-86) adults, in the five younger MDD adults, areal fraction and packing density were smaller than the smallest values of the control subjects. In contrast, among older MDD subjects these parameters tended to be greater than in the older control subjects.

CONCLUSIONS

The present results suggest that the GFAP-immunoreactive astroglia is differentially involved in the pathology of MDD in younger compared with older adults.

Effects of age on gene expression during estrogen-induced synaptic sprouting in the female rat

Age and estrogen treatment influenced fiber outgrowth and compensatory neuronal sprouting after unilateral entorhinal cortex lesions (ECL) which model Alzheimer disease-like deafferentation in the dentate gyrus of the hippocampus. In young F344 rats (3 months old), ovariectomy (OVX) decreased reactive fiber outgrowth by 60%. Sprouting in middle-aged rats (18 months old) was reduced in intact females; no further reduction was caused by OVX. Several astrocyte mRNAs were measured in the dentate gyrus of young and middle-aged female rats in three different estrogen states (sham OVX, OVX, or OVX + estradiol) 1 week after ECL. Glial fibrillary acidic protein (GFAP) mRNA was twofold greater in middle-aged rats than young, although both ages showed threefold increases in response to ECL. In prior studies GFAP was found to be decreased by estradiol treatment 3-4 days after ECL; in this study GFAP mRNA had returned to sham OVX levels in young rats by 7 days post-ECL. Surprisingly, estradiol treatment increased GFAP mRNA levels by 25% above OVX in middle-aged rats. Apolipoprotein E (apoE) mRNA was decreased 20% by age in the dentate, although both age groups showed a 25% increase in apoE mRNA in response to ECL. Apolipoprotein J (apoJ) mRNA was increased 20% in the dentate gyrus of middle-aged rats, and both age groups responded to ECL with a 65% increase in apoJ mRNA. The estrogen state did not alter levels of either apolipoprotein mRNA in the deafferented dentate. The data suggest that the estrogen-induced decrease of GFAP in response to lesions does not persist at 7 days post-ECL during sprouting. Overall effects of age on the dentate gyrus include elevated GFAP mRNA and decreased apoE mRNA. The cortical wound site showed consistent enhancement of GFAP mRNA in both age groups by estradiol above sham OVX and greater responses in middle-aged rats.

Evidence for enhanced neuro-inflammatory processes in neurodegenerative diseases and the action of nitrones as potential therapeutics

A brief review is presented on observations leading to the current notions regarding neuro-inflammatory processes. The greatest focus is on Alzheimer's disease (AD) since this is where the most convincing data has been obtained. A brief summary of observations on the neuroprotective action of alpha-phenyl-tert-butyl-nitrone (PBN) as well as results of research designed to understand its mechanism of action is presented. We hypothesize that the mechanism of action of PBN involves inhibition of signal transduction processes, which are involved in the upregulation of genes mediated by pro-inflammatory cytokines and H2O2 that cause formation of toxic gene products. Results from recent experiments on Kainic acid (KA) mediated brain damage are provided to suggest the validity of the in vivo action of PBN to inhibit neuro-inflammatory processes. The accumulating scientific facts are helping to provide concepts that may become the basis for novel therapeutic approaches to the treatment of several neurodegenerative diseases.

Increased microglial activation and protein nitration in white matter of the aging monkey

Activated microglia are important pathological features of a variety of neurological diseases, including the normal aging process of the brain. Here, we quantified the level of microglial activation in the aging rhesus monkey using antibodies to HLA-DR and inducible nitric oxide synthase (iNOS). We observed that 3 out of 5 white matter areas but only 1 of 4 cortical gray matter regions examined showed significant increases in two measures of activated microglia with age, indicating that diffuse white matter microglial activation without significant gray matter involvement occurs with age. Substantial levels of iNOS and 3-nitrotyrosine, a marker for peroxynitrite, increased diffusely throughout subcortical white matter with age, suggesting a potential role of nitric oxide in age-related white matter injury. In addition, we found that the density of activated microglia in the subcortical white matter of the cingulate gyrus and the corpus callosum was significantly elevated with cognitive impairment in elderly monkeys. This study suggests that microglial activation increases in white matter with age and that these increases may reflect the role of activated microglia in the general pathogenesis of normal brain aging.

The evolution of Alzheimer disease, the reproductive schedule, and apoE isoforms

Alzheimer disease (AD)-like neuropathology increases progressively during aging in most primates, and, in some species, is concurrent with reproductive decline in females and cognitive impairments. We consider how the schedule of AD may have evolved in early humans in relation to the apolipoprotein E (apoE) allele system, which is not found in other primates, and to the increasing duration of postnatal care. The delay of independence and the increasing length of maturation required that the schedule of AD-like neurodegeneration be slowed, otherwise parental caregivers would already have become impaired. We hypothesize that the uniquely human apoE epsilon3 allele evolved from the epsilon4 of primate ancestors during human evolution in relation to the rapid increases of brain size and the emergence of grandmothering. In discussing theses possibilities, we review the diverse bioactivities of apoE, which include involvement in hormone systems. The evolution of menopause is also considered in relation to the protective effect of estrogen on AD.

Infrastructure for research on aging rodents: need for regional facilities to support transgenic studies on aging

I propose that North American investigators who depend largely on individual external grants would benefit from the creation of regional facilities designed to support studies of aging in transgenic models. In general, academic institutions cannot achieve the most cost effectiveness because their facilities are not designed for industrial-scale cost efficiencies. Regional facilities would also increase the reproducibility of experiments. Transgenic studies of prospective genes that modify the risk of Alzheimer and other outcomes of aging could be carried out under standard conditions of nutrition and caging density, which can influence brain structure and behavior. The regional labs should have a strong Pathology Core, which would go far beyond the resources usually available to academic researchers. A national system of regional facilities with Core labs for characterizing genetics, hormones, and pathology would greatly accelerate progress.

Aging-specific expression of Drosophila hsp22

hsp22 is among the least abundantly expressed Drosophila heat shock (hs) genes during both development and heat stress. In contrast, hsp22 was found to be the most abundantly expressed hs gene during Drosophila aging. During aging, hsp22 RNA was induced 60-fold in the head, with somewhat lower level induction in abdomen and thorax. Induction of the other hs gene RNAs was </=3-fold, except for hsp23, which was induced approximately 5-fold in thorax. hsp22 protein was detected using rat anti-hsp22 polyclonal antisera and was induced >150-fold, with particularly abundant expression in eye tissue. Aging-specific induction of hsp22 was reproduced by hsp22:lacZ fusion reporter constructs in transgenic flies. Analysis of specific promoter mutations in transgenic flies indicated that functional heat shock response elements are required for hsp22 induction during aging. Finally, comparison of hsp22 RNA and protein expression patterns suggests that aging-specific expression of hsp22 is regulated at both the transcriptional and the posttranscriptional levels. Aging-specific induction of hsp22 is discussed with regard to current evolutionary theories of aging.