Glial reaction in the hippocampal formation is highly correlated with aging in human brain

Astrocyte expression of aging-associated markers positively correlates with neurodegeneration in the frontal lobe of the rhesus macaque brain

Introduction

As the population over the age of 65 increases, rates of neurodegenerative disorders and dementias will rise - necessitating further research into the cellular and molecular mechanisms that contribute to brain aging. With the critical importance of astrocytes to neuronal health and functioning, we hypothesized that alterations in astrocyte expression of aging-associated markers p16INK4a (p16) and sirtuin 1 (SIRT1) with age would correlate with increased rates of neurodegeneration, as measured by FluoroJade C (FJC) staining.

Methods

To test this hypothesis, 19 rhesus macaques at the Tulane National Primate Research Center were selected based on the following criteria: archival FFPE CNS tissue available to use, no noted neuropathology, and an age range of 5-30 years. Tissues were cut at 5 μm and stained for GFAP, p16, SIRT1, and FJC, followed by whole-slide imaging and HALO® image analysis for percentage of marker-positive cells and relative intensity of each stain.

Results

We found the percentage of p16+ cells increases with age in total cells and astrocytes of the frontal (p = 0.0021, p = 0.0012 respectively) and temporal (p = 0.0226, p = 0.0203 respectively) lobes, as well as the relative intensity of p16 staining (frontal lobe: p = 0.0060; temporal lobe: p = 0.0269). For SIRT1, we found no correlation with age except for an increase in the relative intensity of SIRT1 in the temporal lobe (p = 0.0033). There was an increase in neurodegeneration, as measured by the percentage of FJC+ cells in the frontal lobe with age (p = 0.0057), as well as in the relative intensity of FJC staining in the frontal (p = 0.0030) and parietal (p = 0.0481) lobes. Importantly, increased p16 and SIRT1 expression in astrocytes correlated with increasing neurodegeneration in the frontal lobe (p = 0.0009, p = 0.0095 respectively).

Discussion

Together, these data suggest that age-associated alterations in astrocytes contribute to neurodegeneration and provide a target for mechanistic studies in the future.

Astrocytes in human central nervous system diseases: a frontier for new therapies

Astroglia are a broad class of neural parenchymal cells primarily dedicated to homoeostasis and defence of the central nervous system (CNS). Astroglia contribute to the pathophysiology of all neurological and neuropsychiatric disorders in ways that can be either beneficial or detrimental to disorder outcome. Pathophysiological changes in astroglia can be primary or secondary and can result in gain or loss of functions. Astroglia respond to external, non-cell autonomous signals associated with any form of CNS pathology by undergoing complex and variable changes in their structure, molecular expression, and function. In addition, internally driven, cell autonomous changes of astroglial innate properties can lead to CNS pathologies. Astroglial pathophysiology is complex, with different pathophysiological cell states and cell phenotypes that are context-specific and vary with disorder, disorder-stage, comorbidities, age, and sex. Here, we classify astroglial pathophysiology into (i) reactive astrogliosis, (ii) astroglial atrophy with loss of function, (iii) astroglial degeneration and death, and (iv) astrocytopathies characterised by aberrant forms that drive disease. We review astroglial pathophysiology across the spectrum of human CNS diseases and disorders, including neurotrauma, stroke, neuroinfection, autoimmune attack and epilepsy, as well as neurodevelopmental, neurodegenerative, metabolic and neuropsychiatric disorders. Characterising cellular and molecular mechanisms of astroglial pathophysiology represents a new frontier to identify novel therapeutic strategies.

Unravelling the Collective Calcium Dynamics of Physiologically Aged Astrocytes under a Hypoxic State In Vitro

Astrocytes serve many functions in the brain related to maintaining nerve tissue homeostasis and regulating neuronal function, including synaptic transmission. It is assumed that astrocytes are crucial players in determining the physiological or pathological outcome of the brain aging process and the development of neurodegenerative diseases. Therefore, studies on the peculiarities of astrocyte physiology and interastrocytic signaling during aging are of utmost importance. Calcium waves are one of the main mechanisms of signal transmission between astrocytes, and in the present study we investigated the features of calcium dynamics in primary cultures of murine cortical astrocytes in physiological aging and hypoxia modeling in vitro. Specifically, we focused on the assessment of calcium network dynamics and the restructuring of the functional network architecture in primary astrocytic cultures. Calcium imaging was performed on days 21 ("young" astrocyte group) and 150 ("old" astrocyte group) of cultures' development in vitro. While the number of active cells and frequency of calcium events were decreased, we observed a reduced degree of correlation in calcium dynamics between neighboring cells, which was accompanied by a reduced number of functionally connected cells with fewer and slower signaling events. At the same time, an increase in the mRNA expression of anti-apoptotic factor Bcl-2 and connexin 43 was observed in "old" astrocytic cultures, which can be considered as a compensatory response of cells with a decreased level of intercellular communication. A hypoxic episode aggravates the depression of the connectivity of calcium dynamics of "young" astrocytes rather than that of "old" ones.

The association of astrogliosis and microglial activation with aging and Alzheimer's disease pathology in the chimpanzee brain

Aging and neurodegenerative disorders, such as Alzheimer's disease (AD), trigger an immune response known as glial activation in the brain. Recent evidence indicates species differences in inflammatory responses to AD pathology, highlighting the need for additional comparative studies to further understand human-specific neuropathologies. In the present study, we report on the occurrence of astrogliosis, microglial activation, and their relationship with age and AD-like pathology in a cohort of male and female chimpanzees (Pan troglodytes). Chimpanzees with severe astrogliosis exhibited widespread upregulation of hypertrophic astrocytes immunoreactive for glial fibrillary acidic protein (GFAP) throughout all layers of the dorsolateral prefrontal cortex and a loss of the interlaminar palisade. In addition, extreme astrogliosis was associated with increased astrocyte density in the absence of significant microglial activation and AD lesions. A shift from decreased resting to increased phagocytotic microglia occurred with aging, although proliferation was absent and no changes in astrogliosis was observed. Vascular amyloid correlated with decreased astrocyte and microglia densities, while tau lesions were associated with morphological changes in microglia and greater total glia density and glia: neuron ratio. These results further our understanding of inflammatory processes within the chimpanzee brain and provide comparative data to improve our understanding of human aging and neuropathological processes.

Biomarkers of aging

Aging biomarkers are a combination of biological parameters to (i) assess age-related changes, (ii) track the physiological aging process, and (iii) predict the transition into a pathological status. Although a broad spectrum of aging biomarkers has been developed, their potential uses and limitations remain poorly characterized. An immediate goal of biomarkers is to help us answer the following three fundamental questions in aging research: How old are we? Why do we get old? And how can we age slower? This review aims to address this need. Here, we summarize our current knowledge of biomarkers developed for cellular, organ, and organismal levels of aging, comprising six pillars: physiological characteristics, medical imaging, histological features, cellular alterations, molecular changes, and secretory factors. To fulfill all these requisites, we propose that aging biomarkers should qualify for being specific, systemic, and clinically relevant.

The neuroimmune system - Where aging and excess alcohol intersect

As the percentage of the global population over age 65 grows, and with it a subpopulation of individuals with alcohol use disorder (AUD), understanding the effect of alcohol on the aged brain is of utmost importance. Neuroinflammation is implicated in both natural aging as well as alcohol use, and its role in alterations to brain morphology and function may be exacerbated in aging individuals who drink alcohol to excess. The neuroimmune response to alcohol in aging is complex. The few studies investigating this issue have reported heightened basal activity and either hypo- or hyper-reactivity to an alcohol challenge. This review of preclinical research will first introduce key players of the immune system, then explore changes in neuroimmune function with aging or alcohol alone, with discussion of vulnerable brain regions, changes in cytokines, and varied reactions of microglia and astrocytes. We will then consider different levels of alcohol exposure, relevant animal models of AUD, and neuroimmune activation by alcohol across the lifespan. By identifying key findings, challenges, and targets for future research, we hope to bring more attention and resources to this underexplored area of inquiry.

The Multifaceted Neurotoxicity of Astrocytes in Ageing and Age-Related Neurodegenerative Diseases: A Translational Perspective

In a healthy physiological context, astrocytes are multitasking cells contributing to central nervous system (CNS) homeostasis, defense, and immunity. In cell culture or rodent models of age-related neurodegenerative diseases (NDDs), such as Alzheimer’s disease (AD) and Parkinson’s disease (PD), numerous studies have shown that astrocytes can adopt neurotoxic phenotypes that could enhance disease progression. Chronic inflammatory responses, oxidative stress, unbalanced phagocytosis, or alteration of their core physiological roles are the main manifestations of their detrimental states. However, if astrocytes are directly involved in brain deterioration by exerting neurotoxic functions in patients with NDDs is still controversial. The large spectrum of NDDs, with often overlapping pathologies, and the technical challenges associated with the study of human brain samples complexify the analysis of astrocyte involvement in specific neurodegenerative cascades. With this review, we aim to provide a translational overview about the multi-facets of astrocyte neurotoxicity ranging from in vitro findings over mouse and human cell-based studies to rodent NDDs research and finally evidence from patient-related research. We also discuss the role of ageing in astrocytes encompassing changes in physiology and response to pathologic stimuli and how this may prime detrimental responses in NDDs. To conclude, we discuss how potentially therapeutic strategies could be adopted to alleviate or reverse astrocytic toxicity and their potential to impact neurodegeneration and dementia progression in patients.

Principles of Astrogliopathology

The role of astrocytes in the nervous system pathology was early on embraced by neuroscientists at end of the nineteenth and the beginning of the twentieth century, only to be pushed aside by neurone-centric dogmas during most of the twentieth century. However, the last decade of the twentieth century and the twenty-first century have brought the astroglial "renaissance", which has put astroglial cells as key players in pathophysiology of most if not all disorders of the nervous system and has regarded astroglia as a fertile ground for therapeutic intervention.Astrocytic contribution to neuropathology can be primary, whereby cell-autonomous changes, such as mutations in gene encoding for glial fibrillary acidic protein, can drive the pathologic progression, in this example, Alexander disease. They can also be secondary, when astrocytes respond to a variety of insults to the nervous tissue. Regardless of their origin, being cell-autonomous or not, changes in astroglia that occur in pathology, that is, astrogliopathology, can be contemporary and arbitrary classified into four forms: (i) reactive astrogliosis, (ii) astrocytic atrophy with loss of function, (iii) pathological remodelling of astrocytes and (iv) astrodegeneration morphologically manifested as clasmatodendrosis. Inevitably, as with any other classification, this classification of astrogliopathology awaits its revision that shall be rooted in new discoveries and concepts.

Bioenergetic Impairment in the Neuro-Glia-Vascular Unit: An Emerging Physiopathology during Aging

An emerging concept termed the "neuro-glia-vascular unit" (NGVU) has been established in recent years to understand the complicated mechanism of multicellular interactions among vascular cells, glial cells, and neurons. It has been proverbially reported that the NGVU is significantly associated with neurodegenerative disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). Physiological aging is an inevitable progression associated with oxidative damage, bioenergetic alterations, mitochondrial dysfunction, and neuroinflammation, which is partially similar to the pathology of AD. Thus, senescence is regarded as the background for the development of neurodegenerative diseases. With the exacerbation of global aging, senescence is an increasingly serious problem in the medical field. In this review, the coupling of each component, including neurons, glial cells, and vascular cells, in the NGVU is described in detail. Then, various mechanisms of age-dependent impairment in each part of the NGVU are discussed. Moreover, the potential bioenergetic alterations between different cell types in the NGVU are highlighted, which seems to be an emerging physiopathology associated with the aged brain. Bioenergetic intervention in the NGVU may be a new direction for studies on delaying or diminishing aging in the future.

The Brain Metabolic Signature in Superagers Using In Vivo 1H-MRS: A Pilot Study

BACKGROUND AND PURPOSE

Youthful memory performance in older adults may reflect an underlying resilience to the conventional pathways of aging. Subjects having this unusual characteristic have been recently termed "superagers." This study aimed to explore the significance of imaging biomarkers acquired by ¹H-MRS to characterize superagers and to differentiate them from their normal-aging peers.

MATERIALS AND METHODS

Fifty-five patients older than 80 years of age were screened using a detailed neuropsychological protocol, and 25 participants, comprising 12 superagers and 13 age-matched controls, were statistically analyzed. We used state-of-the-art 3T ¹H-MR spectroscopy to quantify 18 neurochemicals in the posterior cingulate cortex of our subjects. All ¹H-MR spectroscopy data were analyzed using LCModel. Results were further processed using 2 approaches to investigate the technique accuracy: 1) comparison of the average concentration of metabolites estimated with Cramer-Rao lower bounds <20%; and 2) calculation and comparison of the weighted means of metabolites' concentrations.

RESULTS

The main finding observed was a higher total N-acetyl aspartate concentration in superagers than in age-matched controls using both approaches (P = .02 and P = .03 for the weighted means), reflecting a positive association of total N-acetyl aspartate with higher cognitive performance.

CONCLUSIONS

¹H-MR spectroscopy emerges as a promising technique to unravel neurochemical mechanisms related to cognitive aging in vivo and providing a brain metabolic signature in superagers. This may contribute to monitoring future interventional therapies to avoid or postpone the pathologic processes of aging.

Physiological and Pathological Ageing of Astrocytes in the Human Brain

Ageing is the greatest risk factor for dementia, although physiological ageing by itself does not lead to cognitive decline. In addition to ageing, APOE ε4 is genetically the strongest risk factor for Alzheimer's disease and is highly expressed in astrocytes. There are indications that human astrocytes change with age and upon expression of APOE4. As these glial cells maintain water and ion homeostasis in the brain and regulate neuronal transmission, it is likely that age- and APOE4-related changes in astrocytes have a major impact on brain functioning and play a role in age-related diseases. In this review, we will discuss the molecular and morphological changes of human astrocytes in ageing and the contribution of APOE4. We conclude this review with a discussion on technical issues, innovations, and future perspectives on how to gain more knowledge on astrocytes in the human ageing brain.

Diversity of Reactive Astrogliosis in CNS Pathology: Heterogeneity or Plasticity?

Astrocytes are essential for the development and homeostatic maintenance of the central nervous system (CNS). They are also critical players in the CNS injury response during which they undergo a process referred to as "reactive astrogliosis." Diversity in astrocyte morphology and gene expression, as revealed by transcriptional analysis, is well-recognized and has been reported in several CNS pathologies, including ischemic stroke, CNS demyelination, and traumatic injury. This diversity appears unique to the specific pathology, with significant variance across temporal, topographical, age, and sex-specific variables. Despite this, there is limited functional data corroborating this diversity. Furthermore, as reactive astrocytes display significant environmental-dependent plasticity and fate-mapping data on astrocyte subsets in the adult CNS is limited, it remains unclear whether this diversity represents heterogeneity or plasticity. As astrocytes are important for neuronal survival and CNS function post-injury, establishing to what extent this diversity reflects distinct established heterogeneous astrocyte subpopulations vs. environmentally dependent plasticity within established astrocyte subsets will be critical for guiding therapeutic development. To that end, we review the current state of knowledge on astrocyte diversity in the context of three representative CNS pathologies: ischemic stroke, demyelination, and traumatic injury, with the goal of identifying key limitations in our current knowledge and suggesting future areas of research needed to address them. We suggest that the majority of identified astrocyte diversity in CNS pathologies to date represents plasticity in response to dynamically changing post-injury environments as opposed to heterogeneity, an important consideration for the understanding of disease pathogenesis and the development of therapeutic interventions.

Longitudinal quantification of metabolites and macromolecules reveals age- and sex-related changes in the healthy Fischer 344 rat brain

Normal aging is associated with numerous biological changes, including altered brain metabolism and tissue chemistry. In vivo characterization of the neurochemical profile during aging is possible using magnetic resonance spectroscopy, a powerful noninvasive technique capable of quantifying brain metabolites involved in physiological processes that become impaired with age. A prominent macromolecular signal underlies those of brain metabolites and is particularly visible at high fields; parameterization of this signal into components improves quantification and expands the number of biomarkers comprising the neurochemical profile. The present study reports, for the first time, the simultaneous absolute quantification of brain metabolites and individual macromolecules in aging male and female Fischer 344 rats, measured longitudinally using proton magnetic resonance spectroscopy at 7 T. We identified age- and sex-related changes in neurochemistry, with prominent differences in metabolites implicated in anaerobic energy metabolism, antioxidant defenses, and neuroprotection, as well as numerous macromolecule changes. These findings contribute to our understanding of the neurobiological processes associated with healthy aging, critical for the proper identification and management of pathologic aging trajectories. This article is part of the Virtual Special Issue titled COGNITIVE NEUROSCIENCE OF HEALTHY AND PATHOLOGICAL AGING. The full issue can be found on ScienceDirect athttps://www.sciencedirect.com/journal/neurobiology-of-aging/special-issue/105379XPWJP.

Roles of astrocytes in response to aging, Alzheimer's disease and multiple sclerosis

Astrocytes are traditionally recognized for their multiple roles in support of brain function. However, additional changes in these roles are evident in response to brain diseases. In this review, we highlight positive and negative effects of astrocytes in response to aging, Alzheimer's disease and Multiple Sclerosis. We summarize data suggesting that reactive astrocytes may perform critical functions that might be relevant to the etiology of these conditions. In particular, we relate astrocytes effects to actions on synaptic transmission, cognition, and myelination. We suggest that a better understanding of astrocyte functions and how these become altered in response to aging or disease will lead to the appreciation of these cells as useful therapeutic targets.

Astrocyte dystrophy in ageing brain parallels impaired synaptic plasticity

Little is known about age-dependent changes in structure and function of astrocytes and of the impact of these on the cognitive decline in the senescent brain. The prevalent view on the age-dependent increase in reactive astrogliosis and astrocytic hypertrophy requires scrutiny and detailed analysis. Using two-photon microscopy in conjunction with 3D reconstruction, Sholl and volume fraction analysis, we demonstrate a significant reduction in the number and the length of astrocytic processes, in astrocytic territorial domains and in astrocyte-to-astrocyte coupling in the aged brain. Probing physiology of astrocytes with patch clamp, and Ca2+ imaging revealed deficits in K+ and glutamate clearance and spatiotemporal reorganisation of Ca2+ events in old astrocytes. These changes paralleled impaired synaptic long-term potentiation (LTP) in hippocampal CA1 in old mice. Our findings may explain the astroglial mechanisms of age-dependent decline in learning and memory.

Astroglial asthenia and loss of function, rather than reactivity, contribute to the ageing of the brain

Astroglia represent a class of heterogeneous, in form and function, cells known as astrocytes, which provide for homoeostasis and defence of the central nervous system (CNS). Ageing is associated with morphological and functional remodelling of astrocytes with a prevalence of morphological atrophy and loss of function. In particular, ageing is associated with (i) decrease in astroglial synaptic coverage, (ii) deficits in glutamate and potassium clearance, (iii) reduced astroglial synthesis of synaptogenic factors such as cholesterol, (iv) decrease in aquaporin 4 channels in astroglial endfeet with subsequent decline in the glymphatic clearance, (v) decrease in astroglial metabolic support through the lactate shuttle, (vi) dwindling adult neurogenesis resulting from diminished proliferative capacity of radial stem astrocytes, (vii) decline in the astroglial-vascular coupling and deficient blood-brain barrier and (viii) decrease in astroglial ability to mount reactive astrogliosis. Decrease in reactive capabilities of astroglia are associated with rise of age-dependent neurodegenerative diseases. Astroglial morphology and function can be influenced and improved by lifestyle interventions such as intellectual engagement, social interactions, physical exercise, caloric restriction and healthy diet. These modifications of lifestyle are paramount for cognitive longevity.

Oxidative stress in elderly population: A prevention screening study

Background

Aging is a multifactorial phenomenon, characterized by a progressive decline in the efficiency of biochemical and physiological processes and an increased susceptibility to disease. There is increasing evidence that aging and age‐related disease are correlated with an oxidative stress (OS) condition. The latter is characterized by an imbalance between reactive species (RS), in particular reactive oxygen species (ROS) and antioxidant reserve.

Objectives

The aim of this study is to evaluate the two main markers of oxidative stress, plasmatic peroxide concentration (through d‐ROMs FAST test, derivates‐Reactive Oxygen Metabolites) and plasmatic antioxidant power measured by iron‐reducing power (PAT test, Plasma Antioxidant Test) in 290 apparently healthy volunteers over 60, and their possible correlation with age and gender.

Materials and methods

Human capillary blood samples from healthy volunteers were used in this observational study for the evaluation of the markers of OS.

Results

The data obtained broadly demonstrate that the majority of elderly people display an OS condition characterized by increased levels of peroxides and a slight reduction in antioxidant reserve.

Conclusions

Seniors have a greater propensity to develop a condition of oxidative stress, and therefore it is important to associate the monitoring of oxidative stress markers and, if necessary, antioxidant supplementation, with a healthy lifestyle.

Glia: victims or villains of the aging brain?

Aging is the strongest risk factor for metabolic, vascular and neurodegenerative diseases. Aging alone is associated with a gradual decline of cognitive and motor functions. Considering an increasing elderly population in the last century, understanding the cellular and molecular mechanisms contributing to brain aging is of vital importance. Recent genetic and transcriptomic findings strongly suggest that glia are the first cells changing with aging. Glial cells constitute around 50% of the total cells in the brain and play key roles regulating brain homeostasis in health and disease. Their essential functions include providing nutritional support to neurons, activation of immune responses, and regulation of synaptic transmission and plasticity. In this review we discuss how glia are altered in the aging brain and whether these alterations are protective or contribute to the age-related pathological cascade. We focus on the major morphological, transcriptional and functional changes affecting glia in a range of systems, including human, non-human primates, and rodents. We also highlight future directions for investigating the roles of glia in brain aging.

Regional Gene Expression of Inflammation and Oxidative Stress Responses Does Not Predict Neurodegeneration in Aging

Brain aging is accompanied by increased oxidative stress and what has been termed "neuroinflammation," which might contribute to age-related neurodegenerative diseases. We analyzed expression in the transcription of innate inflammatory response genes in eleven representative regions including frontal, parietal, inferior temporal, cingulate, occipital, entorhinal cortex, caudate, putamen, thalamus, substantia nigra, and cerebellar vermis in aging human brains. We probed members of the complement system, colony stimulating factor receptors, toll-like receptors, and pro- and anti-inflammatory cytokines in the brains of subjects with no neurological disease and neurofibrillary tangles (mean age: 47.1  ±  5.7 years) and those with no neurological disease and neurofibrillary pathology stages I-II (mean age: 70.6  ±  6.3 years). Although the entorhinal and frontal cortex were most altered, gene regulation patterns did not match regions with increased vulnerability. Analysis of false discovery rate thresholds revealed no differences for any gene in any region between the 2 groups, including cases in which individual comparisons analyzed using Student t or nonparametric tests showed apparent differences between groups. Moreover, gene expression of major anti-oxidative stress responses did not match neuroinflammation in aging or increased regional susceptibility to major neurodegenerative diseases.

Increased macrophages and changed brain endothelial cell gene expression in the frontal cortex of people with schizophrenia displaying inflammation

Elevated pro-inflammatory cytokines exist in both blood and brain of people with schizophrenia but how this affects molecular indices of the blood-brain barrier (BBB) is unclear. Eight mRNAs relating to BBB function, a microglia and three immune cell markers were measured by qPCR in the prefrontal cortex from 37 people with schizophrenia/schizoaffective disorder and 37 matched controls. This cohort was previously grouped into "high inflammation" and "low inflammation" subgroups based on cortical inflammatory-related transcripts. Soluble intercellular adhesion molecule-1 (sICAM1) was measured in the plasma of 78 patients with schizophrenia/schizoaffective disorder and 73 healthy controls. We found that sICAM1 was significantly elevated in schizophrenia. An efflux transporter, ABCG2, was lower, while mRNAs encoding VE-cadherin and ICAM1 were higher in schizophrenia brain. The "high inflammation" schizophrenia subgroup had lower ABCG2 and higher ICAM1, VE-cadherin, occludin and interferon-induced transmembrane protein mRNAs compared to both "low inflammation" schizophrenia and "low inflammation" control subgroups. ICAM1 immunohistochemistry showed enrichment in brain endothelium regardless of diagnosis and was localised to astrocytes in some brains. Microglia mRNA was not altered in schizophrenia nor did it correlate with ICAM1 expression. Immune cell mRNAs were elevated in "high inflammation" schizophrenia compared to both "low inflammation" schizophrenia and controls. CD163+ perivascular macrophages were identified by immunohistochemistry in brain parenchyma in over 40% of "high inflammation" schizophrenia brains. People with high levels of cytokine expression and schizophrenia display changes consistent with greater immune cell transmigration into brain via increased ICAM1, which could contribute to other neuropathological changes found in this subgroup of people.

Neuroinflammation in frontotemporal dementia

Frontotemporal dementia (FTD) refers to a group of progressive neurodegenerative disorders with different pathological signatures, genetic variability and complex disease mechanisms, for which no effective treatments exist. Despite advances in understanding the underlying pathology of FTD, sensitive and specific fluid biomarkers for this disease are lacking. As in other types of dementia, mounting evidence suggests that neuroinflammation is involved in the progression of FTD, including cortical inflammation, microglial activation, astrogliosis and differential expression of inflammation-related proteins in the periphery. Furthermore, an overlap between FTD and autoimmune disease has been identified. The most substantial evidence, however, comes from genetic studies, and several FTD-related genes are also implicated in neuroinflammation. This Review discusses specific evidence of neuroinflammatory mechanisms in FTD and describes how advances in our understanding of these mechanisms, in FTD as well as in other neurodegenerative diseases, might facilitate the development and implementation of diagnostic tools and disease-modifying treatments for FTD.

Astrocyte Function Is Affected by Aging and Not Alzheimer's Disease: A Preliminary Investigation in Hippocampi of 3xTg-AD Mice

Old age is a risk factor for Alzheimer's disease (AD), which is characterized by hippocampal impairment together with substantial changes in glial cell functions. Are these alterations due to the disease progression or are they a consequence of aging? To start addressing this issue, we studied the expression of specific astrocytic and microglial structural and functional proteins in a validated transgenic model of AD (3×Tg-AD). These mice develop both amyloid plaques and neurofibrillary tangles, and initial signs of the AD-like pathology have been documented as early as three months of age. We compared male 3×Tg-AD mice at 6 and 12 months of age with their wild-type age-matched counterparts. We also investigated neurons by examining the expression of both the microtubule-associated protein 2 (MAP2), a neuronal structural protein, and the brain-derived neurotrophic factor (BDNF). The latter is indeed a crucial indicator for synaptic plasticity and neurogenesis/neurodegeneration. Our results show that astrocytes are more susceptible to aging than microglia, regardless of mouse genotype. Moreover, we discovered significant age-dependent alterations in the expression of proteins responsible for astrocyte-astrocyte and astrocyte-neuron communication, as well as a significant age-dependent decline in BDNF expression. Our data promote further research on the unexplored role of astroglia in both physiological and pathological aging.

Astrocytic changes with aging and Alzheimer's disease-type pathology in chimpanzees

Astrocytes are the main homeostatic cell of the central nervous system. In addition, astrocytes mediate an inflammatory response when reactive to injury or disease known as astrogliosis. Astrogliosis is marked by an increased expression of glial fibrillary acidic protein (GFAP) and cellular hypertrophy. Some degree of astrogliosis is associated with normal aging and degenerative conditions such as Alzheimer's disease (AD) and other dementing illnesses in humans. The recent observation of pathological markers of AD (amyloid plaques and neurofibrillary tangles) in aged chimpanzee brains provided an opportunity to examine the relationships among aging, AD-type pathology, and astrocyte activation in our closest living relatives. Stereologic methods were used to quantify GFAP-immunoreactive astrocyte density and soma volume in layers I, III, and V of the prefrontal and middle temporal cortex, as well as in hippocampal fields CA1 and CA3. We found that the patterns of astrocyte activation in the aged chimpanzee brain are distinct from humans. GFAP expression does not increase with age in chimpanzees, possibly indicative of lower oxidative stress loads. Similar to humans, chimpanzee layer I astrocytes in the prefrontal cortex are susceptible to AD-like changes. Both prefrontal cortex layer I and hippocampal astrocytes exhibit a high degree of astrogliosis that is positively correlated with accumulation of amyloid beta and tau proteins. However, unlike humans, chimpanzees do not display astrogliosis in other cortical layers. These results demonstrate a unique pattern of cortical aging in chimpanzees and suggest that inflammatory processes may differ between humans and chimpanzees in response to pathology.

Astrocyte Heterogeneity: Impact to Brain Aging and Disease

Astrocytes, one of the largest glial cell population in the central nervous system (CNS), play a key function in several events of brain development and function, such as synapse formation and function, control of neurotransmitters release and uptake, production of trophic factors and control of neuronal survival. Initially described as a homogenous population, several evidences have pointed that astrocytes are highly heterogeneous, both morphologically and functionally, within the same region, and across different brain regions. Recent findings suggest that the heterogeneity in the expression profile of proteins involved in astrocyte function may predict the selective vulnerability of brain regions to specific diseases, as well as to the age-related cognitive decline. However, the molecular mechanisms underlying these changes, either in aging as well as in brain disease are scarce. Neuroinflammation, a hallmark of several neurodegenerative diseases and aging, is reported to have a dubious impact on glial activation, as these cells release pro- and anti-inflammatory cytokines and chemokines, anti-oxidants, free radicals, and neurotrophic factors. Despite the emerging evidences supporting that reactive astrocytes have a duality in their phenotype, neurotoxic or neuroprotective properties, depending on the age and stimuli, the underlying mechanisms of their activation, cellular interplays and the impact of regional astrocyte heterogeneity are still a matter of discussion. In this review article, we will summarize recent findings on astrocyte heterogeneity and phenotypes, as well as their likely impact for the brain function during aging and neural diseases. We will focus on the molecules and mechanisms triggered by astrocyte to control synapse formation in different brain regions. Finally, we will discuss new evidences on how the modulation of astrocyte phenotype and function could impact the synaptic deficits and glial dysfunction present in aging and pathological states.

Neuroglia in Ageing

Ageing reduces the functional capacity of all organs, so does that of the nervous system; the latter is evident in the reduction of cognitive abilities, learning and memory. While the exact mechanisms of ageing of the nervous system remain elusive, it is without doubt that morpho-functional changes in a variety of neuroglial cells contribute to this process. The age-dependent changes in neuroglia are characterised by a progressive loss of function. This reduces glial ability to homeostatically nurture, protect and regenerate the nervous tissue. Such neuroglial paralysis also facilitates neurodegenerative processes. Ageing of neuroglia is variable and can be affected by environmental factors and comorbidities.

Astrocyte activation and reactive gliosis-A new target in stroke?

Stroke is an acute insult to the central nervous system (CNS) that triggers a sequence of responses in the acute, subacute as well as later stages, with prominent involvement of astrocytes. Astrocyte activation and reactive gliosis in the acute stage of stroke limit the tissue damage and contribute to the restoration of homeostasis. Astrocytes also control many aspects of neural plasticity that is the basis for functional recovery. Here, we discuss the concept of intermediate filaments (nanofilaments) and the complement system as two handles on the astrocyte responses to injury that both present attractive opportunities for novel treatment strategies modulating astrocyte functions and reactive gliosis.

Altered Gene Expression in Prefrontal Cortex of a Fabry Disease Mouse Model

Fabry disease is an X-chromosome linked hereditary disease that is caused by loss of function mutations in the α-galactosidase A (α-Gal A) gene, resulting in defective glycolipid degradation and subsequent accumulation of globotriaosylceramide (Gb3) in different tissues, including vascular endothelial cells and neurons in the peripheral and central nervous system. We recently reported a differential gene expression profile of α-Gal A^(−/0) mouse dorsal root ganglia, an established animal model of Fabry disease, thereby providing new gene targets that might underlie the neuropathic pain related symptoms. To investigate the cognitive symptoms experienced by Fabry patients, we performed one-color based hybridization microarray expression profiling of prefrontal cortex samples from adult α-Gal A^(−/0) mice and age-matched wildtype controls, followed by protein-protein interaction and pathway analyses for the differentially regulated mRNAs. We found that from a total of 381 differentially expressed genes, 135 genes were significantly upregulated, whereas 246 genes were significantly downregulated between α-Gal A^(−/0) mice and wildtype controls. Enrichment analysis for downregulated genes revealed mainly immune related pathways, including immune/defense responses, regulation of cytokine production, as well as signaling and transport regulation pathways. Further analysis of the regulated genes revealed a large number of genes involved in neurodegeneration. The current analysis for the first time presents a differential gene expression profile of central nervous system tissue from α-Gal A^(−/0) mice, thereby providing novel knowledge on the deregulation and a possible contribution of gene expression to Fabry disease related brain pathologies.

Inosine improves cognitive function and decreases aging-induced oxidative stress and neuroinflammation in aged female rats

In the present study, the effect of inosine was evaluated on learning and memory of 18 months old aged female rats. Inosine (50, 100 and 200 mg/kg; i.p.) was administered to separate groups of rats for 15 successive days. Donepezil (1 mg/kg; i.p.), an acetylcholinesterase inhibitor, was used as a standard drug. Behavioral models such as Morris water maze and elevated plus maze were used to evaluate the effect of drugs on learning and memory of rats. After behavioral studies, animals were killed and their brain was isolated and further processed for estimation of various biochemical parameters such as acetylcholinesterase activity, oxidative stress markers, proinflammatory marker and histological examinations. Inosine (100 and 200 mg/kg) significantly improved learning and memory of aged rats. Further, inosine significantly reduced lipid peroxidation and nitrite, and increased the levels of reduced glutathione and superoxide dismutase. However, no significant difference in AChEs activity was observed in inosine-treated rats as compared to aged control rats. TNF-α level was found to be ameliorated in aged rats by inosine. Histopathological evaluation showed that inosine-treated aged rats have less number of pyknotic neurons in hippocampal CA1 region as compared to aged control rats. In conclusion, inosine significantly improved learning and memory of aged female rats possibly through its antioxidant as well as anti-inflammatory effect and improvement of neuronal survival in the hippocampal CA1 region. However, additional studies are required to further explore the downstream signaling pathways involved in the neuroprotective effect of inosine in aged animals.

Evidence for reduced neurogenesis in the aging human hippocampus despite stable stem cell markers

Reduced neurogenesis in the aging mammalian hippocampus has been linked to cognitive deficits and increased risk of dementia. We utilized postmortem human hippocampal tissue from 26 subjects aged 18–88 years to investigate changes in expression of six genes representing different stages of neurogenesis across the healthy adult lifespan. Progressive and significant decreases in mRNA levels of the proliferation marker Ki67 (MKI67) and the immature neuronal marker doublecortin (DCX) were found in the healthy human hippocampus over the lifespan. In contrast, expression of genes for the stem cell marker glial fibrillary acidic protein delta and the neuronal progenitor marker eomesodermin was unchanged with age. These data are consistent with a persistence of the hippocampal stem cell population with age. Age‐associated expression of the proliferation and immature neuron markers MKI67 and DCX, respectively, was unrelated, suggesting that neurogenesis‐associated processes are independently altered at these points in the development from stem cell to neuron. These data are the first to demonstrate normal age‐related decreases at specific stages of adult human hippocampal neurogenesis.

Resilient protein co-expression network in male orbitofrontal cortex layer 2/3 during human aging

The orbitofrontal cortex (OFC) is vulnerable to normal and pathologic aging. Currently, layer resolution large-scale proteomic studies describing "normal" age-related alterations at OFC are not available. Here, we performed a large-scale exploratory high-throughput mass spectrometry-based protein analysis on OFC layer 2/3 from 15 "young" (15-43 years) and 18 "old" (62-88 years) human male subjects. We detected 4193 proteins and identified 127 differentially expressed (DE) proteins (p-value ≤0.05; effect size >20%), including 65 up- and 62 downregulated proteins (e.g., GFAP, CALB1). Using a previously described categorization of biological aging based on somatic tissues, that is, peripheral "hallmarks of aging," and considering overlap in protein function, we show the highest representation of altered cell-cell communication (54%), deregulated nutrient sensing (39%), and loss of proteostasis (35%) in the set of OFC layer 2/3 DE proteins. DE proteins also showed a significant association with several neurologic disorders; for example, Alzheimer's disease and schizophrenia. Notably, despite age-related changes in individual protein levels, protein co-expression modules were remarkably conserved across age groups, suggesting robust functional homeostasis. Collectively, these results provide biological insight into aging and associated homeostatic mechanisms that maintain normal brain function with advancing age.

Primary motor cortex alterations in Alzheimer disease: A study in the 3xTg-AD model

INTRODUCTION

In humans and animal models, Alzheimer disease (AD) is characterised by accumulation of amyloid-β peptide (Aβ) and hyperphosphorylated tau protein, neuronal degeneration, and astrocytic gliosis, especially in vulnerable brain regions (hippocampus and cortex). These alterations are associated with cognitive impairment (loss of memory) and non-cognitive impairment (motor impairment). The purpose of this study was to identify cell changes (neurons and glial cells) and aggregation of Aβ and hyperphosphorylated tau protein in the primary motor cortex (M1) in 3xTg-AD mouse models at an intermediate stage of AD.

METHODS

We used female 3xTg-AD mice aged 11 months and compared them to non-transgenic mice of the same age. In both groups, we assessed motor performance (open field test) and neuronal damage in M1 using specific markers: BAM10 (extracellular Aβ aggregates), tau 499 (hyperphosphorylated tau protein), GFAP (astrocytes), and Klüver-Barrera staining (neurons).

RESULTS

Female 3xTg-AD mice in intermediate stages of the disease displayed motor and cellular alterations associated with Aβ and hyperphosphorylated tau protein deposition in M1.

CONCLUSIONS

Patients with AD display signs and symptoms of functional impairment from early stages. According to our results, M1 cell damage in intermediate-stage AD affects motor function, which is linked to progression of the disease.

The Immunomodulatory Effects of Plant Extracts and Plant Secondary Metabolites on Chronic Neuroinflammation and Cognitive Aging: A Mechanistic and Empirical Review

Advances in healthcare have considerably improved the life expectancy of the human population over the last century and this has brought about new challenges. As we live longer the capacity for cognitive aging increases. Consequently, it has been noted that decline in cognitive performance in the elderly in domains of reasoning, problem solving skills, attention, processing speed, working memory and episodic memory is a significant societal problem. Despite the enormity of this issue there are relatively few interventions for cognitive aging. This may be due to our current state of knowledge on biological factors that underpin cognitive aging. One of the biological contributors to cognitive aging is chronic neuroinflammation. This review will provide an overview of the peripheral and central mechanisms involved in chronic neuroinflammation and how neuroinflammation may be related to age-associated cognitive decline. Plant based extracts including herbal and nutritional supplements with anti-inflammatory properties will be examined in relation to their utility in treating age-related cognitive decline. Plant based extracts in particular offer interesting pharmacological properties that may be quickly utilized to prevent cognitive aging.

Longitudinal imaging reveals subhippocampal dynamics in glutamate levels associated with histopathologic events in a mouse model of tauopathy and healthy mice

Tauopathies are neurodegenerative disorders characterized by abnormal intracellular aggregates of tau protein, and include Alzheimer's disease, corticobasal degeneration, frontotemporal dementia, and traumatic brain injury. Glutamate metabolism is altered in neurodegenerative disorders manifesting in higher or lower concentrations of glutamate, its transporters or receptors. Previously, glutamate chemical exchange saturation transfer (GluCEST) magnetic resonance imaging (MRI) demonstrated that glutamate levels are reduced in regions of synapse loss in the hippocampus of a mouse model of late-stage tauopathy. We performed a longitudinal GluCEST imaging experiment paired with a cross-sectional study of histologic markers of tauopathy to determine whether (1) early GluCEST changes are associated with synapse loss before volume loss occurs in the hippocampus, and whether (2) subhippocampal dynamics in GluCEST are associated with histopathologic events related to glutamate alterations in tauopathy. Live imaging of the hippocampus in three serial slices was performed without exogenous contrast agents, and subregions were segmented based on a k-means cluster model. Subregions of the hippocampus were analyzed (cornu ammonis CA1, CA3, dentate gyrus DG, and ventricle) in order to associate local MRI-observable changes in glutamate with histological measures of glial cell proliferation (GFAP), synapse density (synaptophysin, VGlut1) and glutamate receptor (NMDA-NR1) levels. Early differences in GluCEST between healthy and tauopathy mice were measured in the CA1 and DG subregions (30% reduction, P ≤ 0.001). Synapse density was also significantly reduced in every subregion of the hippocampus in tauopathy mice by 6 months. Volume was not significantly reduced in any subregion until 13 months. Further, a gradient in glutamate levels was observed in vivo along hippocampal axes that became polarized as tauopathy progressed. Dynamics in hippocampal glutamate levels throughout lifetime were most closely correlated with combined changes in synaptophysin and GFAP, indicating that GluCEST imaging may be a surrogate marker of glutamate concentration in glial cells and at the synaptic level. © 2016 Wiley Periodicals, Inc.

Astrocyte elevated gene-1 (AEG-1) and the A(E)Ging HIV/AIDS-HAND

Recent attempts to analyze human immunodeficiency virus (HIV)-1-induced gene expression changes in astrocytes uncovered a multifunctional oncogene, astrocyte elevated gene-1 (AEG-1). Our previous studies revealed that AEG-1 regulates reactive astrocytes proliferation, migration and inflammation, hallmarks of aging and CNS injury. Moreover, the involvement of AEG-1 in neurodegenerative disorders, such as Huntington's disease and migraine, and its induction in the aged brain suggest a plausible role in regulating overall CNS homeostasis and aging. Therefore, it is important to investigate AEG-1 specifically in aging-associated cognitive decline. In this study, we decipher the common mechanistic links in cancer, aging and HIV-1-associated neurocognitive disorders that likely contribute to AEG-1-based regulation of astrocyte responses and function. Despite AEG-1 incorporation into HIV-1 virions and its induction by HIV-1, tumor necrosis factor-α and interleukin-1β, the specific role(s) of AEG-1 in astrocyte-driven HIV-1 neuropathogenesis are incompletely defined. We propose that AEG-1 plays a central role in a multitude of cellular stress responses involving mitochondria, endoplasmic reticulum and the nucleolus. It is thus important to further investigate AEG-1-based cellular and molecular regulation in order to successfully develop better therapeutic approaches that target AEG-1 to combat cancer, HIV-1 and aging.

Variable laterality of corticospinal tract axons that regenerate after spinal cord injury as a result of PTEN deletion or knock-down

Corticospinal tract (CST) axons from one hemisphere normally extend and terminate predominantly in the contralateral spinal cord. We previously showed that deleting the gene phosphatase and tensin homolog (PTEN) in the sensorimotor cortex enables CST axons to regenerate after spinal cord injury and that some regenerating axons extend along the "wrong" side. Here, we characterize the degree of specificity of regrowth in terms of laterality. PTEN was selectively deleted via cortical adeno-associated virus (AAV)-Cre injections in neonatal PTEN-floxed mice. As adults, mice received dorsal hemisection injuries at T12 or complete crush injuries at T9. CST axons from one hemisphere were traced by unilateral biotinylated dextran amine (BDA) injections in PTEN-deleted mice with spinal cord injury and in noninjured PTEN-floxed mice that had not received AAV-Cre. In noninjured mice, 97.9 ± 0.7% of BDA-labeled axons in white matter and 88.5 ± 1.0% of BDA-labeled axons in gray matter were contralateral to the cortex of origin. In contrast, laterality of CST axons that extended past a lesion due to PTEN deletion varied across animals. In some cases, regenerated axons extended predominantly on the ipsilateral side; in other cases, axons extended predominantly contralaterally, and in others, axons were similar in numbers on both sides. Similar results were seen in analyses of cases from previous studies using short hairpin (sh)RNA-mediated PTEN knock-down. These results indicate that CST axons that extend past a lesion due to PTEN deletion or knock-down do not maintain the contralateral rule of the noninjured CST, highlighting one aspect of how the resultant circuitry from regenerating axons may differ from that of the uninjured CST. J. Comp. Neurol. 524:2654-2676, 2016. © 2016 Wiley Periodicals, Inc.

Low levels of aluminum can lead to behavioral and morphological changes associated with Alzheimer's disease and age-related neurodegeneration

Aluminum (Al) is a very common component of the earth's mineral composition. It is not essential element for life and is a constituent of rather inert minerals. Therefore, it has often been regarded as not presenting a significant health hazard. As a result, aluminum-containing agents been used in the preparation of many foodstuffs processing steps and also in elimination of particulate organic matter from water. More recently, the reduced pH of bodies of water resulting from acid rain has led to mobilization of aluminum-containing minerals into a more soluble form, and these have thus entered residential drinking water resources. By this means, the body burden of aluminum in humans has increased. Epidemiological and experimental findings indicate that aluminum is not as harmless as was previously thought, and that aluminum may contribute to the inception and advancement of Alzheimer's disease. Epidemiological data is reinforced by indications that aluminum exposure can result in excess inflammatory activity within the brain. Activation of the immune system not initiated by an infectious agent, typifies the aging brain and is even more augmented in several neurodegenerative diseases. The origin of most age-related neurological disorders is generally not known but as they are largely not of genetic derivation, their development is likely triggered by unknown environmental factors. There is a growing and consistent body of evidence that points to aluminum as being one such significant influence. Evidence is presented that reinforces the likelihood that aluminum is a factor speeding the rate of brain aging. Such acceleration would inevitably enlarge the incidence of age-related neurological diseases.

Impact of age-related neuroglial cell responses on hippocampal deterioration

Aging is one of the greatest risk factors for the development of sporadic age-related neurodegenerative diseases and neuroinflammation is a common feature of this disease phenotype. In the immunoprivileged brain, neuroglial cells, which mediate neuroinflammatory responses, are influenced by the physiological factors in the microenvironment of the central nervous system (CNS). These physiological factors include but are not limited to cell-to-cell communication involving cell adhesion molecules, neuronal electrical activity and neurotransmitter and neuromodulator action. However, despite this dynamic control of neuroglial activity, in the healthy aged brain there is an alteration in the underlying neuroinflammatory response notably seen in the hippocampus, typified by astrocyte/microglia activation and increased pro-inflammatory cytokine production and signaling. These changes may occur without any overt concurrent pathology, however, they typically correlate with deteriorations in hippocamapal or cognitive function. In this review we examine two important phenomenons, firstly the relationship between age-related brain deterioration (focusing on hippocampal function) and underlying neuroglial response(s), and secondly how the latter affects molecular and cellular processes within the hippocampus that makes it vulnerable to age-related cognitive decline.

Natural therapeutic agents for neurodegenerative diseases from a traditional herbal medicine Pongamia pinnata (L.) Pierre

Neurodegenerative diseases are associated with neuroinflammation, manifested by over-production of nitric oxide (NO) by microglial cells. Now there still lack effective treatment and prevention for the neurodegenerative diseases. Concerning neuroinflammation mediated by microglia cell, bioactivity-guided phytochemical research of Pongamia pinnata (L.) Pierre was performed in this study. A new chlorinated flavonoid, 2′,6′-dichlore-3′, 5′-dimethoxy-[2′′,3′′:7,8]-furanoflavone (1) was identified together with 29 known compounds, including flavonoids (compounds 2-17), isoflavonoids (compounds 18-23), chalcones (compounds 24-25), flavonones (compounds 26-27), triterpenes (28-29) and alkaloid (30) from the effective dichloride methane extract of dry stem of P. pinnata (L.) Pierre. Their structures were elucidated by physicochemical and spectral methods. The anti-neuroinflammatory activities were assayed in BV-2 cells by assessing LPS-induced NO production. Then pongaglabol methyl ether (2), lonchocarpin (24) and glabrachromene II (25) were selected as potential therapeutic agents for neurodegenerative diseases because of their significant anti-neuroinflammatory activities. Furthermore, the characteristics of structure type existing in P. pinnata (L.) Pierre and brief SAR were summarized, respectively.

Prolonged neuroinflammation after lipopolysaccharide exposure in aged rats

Inflammation is a hallmark of several disease states ranging from neurodegeneration to sepsis but is also implicated in physiological processes like ageing. Non-resolving inflammation and prolonged neuroinflammation are unclear processes implicated in several conditions, including ageing. In this study we studied the long-term effects of endotoxemia, as systemic lipopolysaccharide (LPS) injection, focusing on the role of astrocyte activation and cytokine release in the brain of aged rats. A single dose of LPS (2 mg/kg) or 0.9% saline was injected intraperitoneally in aged rats. Levels of pro-inflammatory cytokines (TNFα and IL-1β) and NF-κB p65 activation were measured systemically and in hippocampal tissue. Astrocytes and cytokines release in the CNS were detected via double immunofluorescence staining at different time-points up to day 30. Serum levels of TNFα and IL-1β were significantly increased acutely after 30 minutes (p<0.001) and up to 6 hours (p<0.001) following LPS-injection. Centrally, LPS-treated rats showed up-regulated mRNA expression and protein levels of pro-inflammatory cytokines in the hippocampus. These changes associated with astrogliosis in the hippocampus dentate gyrus (DG), IL-1β immunoreactivity and elevated NF-κB p65 expression up to day 30 post LPS exposure. Overall, these data demonstrate that LPS induces prolonged neuroinflammation and astrocyte activation in the hippocampus of aged rats. Hippocampal NF-κB p65 and excessive astrocytes-derived IL-1β release may play a pivotal role in regulating long-lasting neuroinflammation.

Biochemical assessment of precuneus and posterior cingulate gyrus in the context of brain aging and Alzheimer's disease

Defining the biochemical alterations that occur in the brain during “normal” aging is an important part of understanding the pathophysiology of neurodegenerative diseases and of distinguishing pathological conditions from aging-associated changes. Three groups were selected based on age and on having no evidence of neurological or significant neurodegenerative disease: 1) young adult individuals, average age 26 years (n = 9); 2) middle-aged subjects, average age 59 years (n = 5); 3) oldest-old individuals, average age 93 years (n = 6). Using ELISA and Western blotting methods, we quantified and compared the levels of several key molecules associated with neurodegenerative disease in the precuneus and posterior cingulate gyrus, two brain regions known to exhibit early imaging alterations during the course of Alzheimer’s disease. Our experiments revealed that the bioindicators of emerging brain pathology remained steady or decreased with advancing age. One exception was S100B, which significantly increased with age. Along the process of aging, neurofibrillary tangle deposition increased, even in the absence of amyloid deposition, suggesting the presence of amyloid plaques is not obligatory for their development and that limited tangle density is a part of normal aging. Our study complements a previous assessment of neuropathology in oldest-old subjects, and within the limitations of the small number of individuals involved in the present investigation, it adds valuable information to the molecular and structural heterogeneity observed along the course of aging and dementia. This work underscores the need to examine through direct observation how the processes of amyloid deposition unfold or change prior to the earliest phases of dementia emergence.

Is brain gliosis a characteristic of chronic methamphetamine use in the human?

Animal data show that high doses of the stimulant drug methamphetamine can damage brain dopamine neurones; however, it is still uncertain whether methamphetamine, at any dose, is neurotoxic to human brain. Since gliosis is typically associated with brain damage and is observed in animal models of methamphetamine exposure, we measured protein levels (intact protein and fragments, if any) of markers of microgliosis (glucose transporter-5, human leukocyte antigens HLA-DRα [TAL.1B5] and HLA-DR/DQ/DPβ [CR3/43]) and astrogliosis (glial fibrillary acidic protein, vimentin, and heat shock protein-27) in homogenates of autopsied brain of chronic methamphetamine users (n=20) and matched controls (n=23). Intact protein levels of all markers were, as expected, elevated (+28%-1270%, P<0.05) in putamen of patients with the neurodegenerative disorder multiple system atrophy (as a positive control) as were concentrations of fragments of glial fibrillary acidic protein, vimentin and heat shock protein-27 (+170%-4700%, P<0.005). In contrast, intact protein concentrations of the markers were normal in dopamine-rich striatum (caudate, putamen) and in the frontal cortex of the drug users. However, striatal levels of cleaved vimentin and heat shock protein-27 were increased (by 98%-211%, P<0.05), with positive correlations (r=0.41-0.60) observed between concentrations of truncated heat shock protein-27 and extent of dopamine loss (P=0.006) and levels of lipid peroxidation products 4-hydroxynonenal (P=0.046) and malondialdehyde (P=0.11). Our failure to detect increased intact protein levels of commonly used markers of microgliosis and astrogliosis could be explained by exposure to methamphetamine insufficient to cause a toxic process associated with overt gliosis; however, about half of the subjects had died of drug intoxication suggesting that "high" drug doses might have been used. Alternatively, drug tolerance to toxic effects might have occurred in the subjects, who were all chronic methamphetamine users. Nevertheless, the finding of above-normal levels of striatal vimentin and heat shock protein-27 fragments (which constituted 10-28% of the intact protein), for which changes in the latter correlated with those of several markers possibly suggestive of damage, does suggest that some astrocytic "disturbance" had occurred, which might in principle be related to methamphetamine neurotoxicity or to a neuroplastic remodeling process. Taken together, our neurochemical findings do not provide strong evidence for either marked microgliosis or astrogliosis in at least a subgroup of human recreational methamphetamine users who used the drug chronically and shortly before death. However, a logistically more difficult quantitative histopathological study is needed to confirm whether glial changes occur or do not occur in brain of human methamphetamine (and amphetamine) users.

High-field proton magnetic resonance spectroscopy reveals metabolic effects of normal brain aging

Altered brain metabolism is likely to be an important contributor to normal cognitive decline and brain pathology in elderly individuals. To characterize the metabolic changes associated with normal brain aging, we used high-field proton magnetic resonance spectroscopy in vivo to quantify 20 neurochemicals in the hippocampus and sensorimotor cortex of young adult and aged rats. We found significant differences in the neurochemical profile of the aged brain when compared with younger adults, including lower aspartate, ascorbate, glutamate, and macromolecules, and higher glucose, myo-inositol, N-acetylaspartylglutamate, total choline, and glutamine. These neurochemical biomarkers point to specific cellular mechanisms that are altered in brain aging, such as bioenergetics, oxidative stress, inflammation, cell membrane turnover, and endogenous neuroprotection. Proton magnetic resonance spectroscopy may be a valuable translational approach for studying mechanisms of brain aging and pathology, and for investigating treatments to preserve or enhance cognitive function in aging.

Prolonged exposure to low levels of aluminum leads to changes associated with brain aging and neurodegeneration

Aluminum is one of the most common metal elements in the earth's crust. It is not an essential element for life and has commonly been thought of as a rather inert and insoluble mineral. Therefore, it has often been regarded as not posing a significant health hazard. In consequence, aluminum-containing agents been used in many food processing steps and also in removal by flocculation of particulate organic matter from water. In recent years, acid rain has tended to mobilize aluminum-containing minerals into a more soluble form, ionic Al(3+), which has found their way into many reservoirs that constitute residential drinking water resources. As a result, the human body burden of aluminum has increased. Epidemiological studies suggest that aluminum may not be as innocuous as was previously thought and that aluminum may actively promote the onset and progression of Alzheimer's disease. Epidemiological data is strengthened by experimental evidence of aluminum exposure leading to excess inflammatory activity within the brain. Such apparently irrelevant immune activity unprovoked by an exogenous infectious agent characterizes the aging brain and is even more pronounced in several neurodegenerative diseases. The causation of most of these age-related neurological disorders is not understood but since they are generally not genetic, one must assume that their development is underlain by unknown environmental factors. There is an increasing and coherent body of evidence that implicates aluminum as being one such significant factor. Evidence is outlined supporting the concept of aluminum's involvement in hastening brain aging. This acceleration would then inevitably lead to increased incidence of specific age-related neurological diseases.

Versatile and simple approach to determine astrocyte territories in mouse neocortex and hippocampus

Background

Besides their neuronal support functions, astrocytes are active partners in neuronal information processing. The typical territorial structure of astrocytes (the volume of neuropil occupied by a single astrocyte) is pivotal for many aspects of glia–neuron interactions.

Methods

Individual astrocyte territorial volumes are measured by Golgi impregnation, and astrocyte densities are determined by S100β immunolabeling. These data are compared with results from conventionally applied methods such as dye filling and determination of the density of astrocyte networks by biocytin loading. Finally, we implemented our new approach to investigate age-related changes in astrocyte territories in the cortex and hippocampus of 5- and 21-month-old mice.

Results

The data obtained by our simplified approach based on Golgi impregnation were compared to previously published dye filling experiments, and yielded remarkably comparable results regarding astrocyte territorial volumes. Moreover, we found that almost all coupled astrocytes (as indicated by biocytin loading) were immunopositive for S100β. A first application of this new experimental approach gives insight in age-dependent changes in astrocyte territorial volumes. They increased with age, while cell densities remained stable. In 5-month-old mice, the overlap factor was close to 1, revealing little or no interdigitation of astrocyte territories. However, in 21-month-old mice, the overlap factor was more than 2, suggesting that processes of adjacent astrocytes interdigitate.

Conclusion

Here we verified the usability of a simple, versatile method for assessing astrocyte territories and the overlap factor between adjacent territories. Second, we found that there is an age-related increase in territorial volumes of astrocytes that leads to loss of the strict organization in non-overlapping territories. Future studies should elucidate the physiological relevance of this adaptive reaction of astrocytes in the aging brain and the methods presented in this study might be a powerful tool to do so.

Insulin-like growth factor-1 in CNS and cerebrovascular aging

Insulin-like growth factor-1 (IGF-1) is an important anabolic hormone that decreases with age. In the past two decades, extensive research has determined that the reduction in IGF-1 is an important component of the age-related decline in cognitive function in multiple species including humans. Deficiency in circulating IGF-1 results in impairment in processing speed and deficiencies in both spatial and working memory. Replacement of IGF-1 or factors that increase IGF-1 to old animals and humans reverses many of these cognitive deficits. Despite the overwhelming evidence for IGF-1 as an important neurotrophic agent, the specific mechanisms through which IGF-1 acts have remained elusive. Recent evidence indicates that IGF-1 is both produced by and has important actions on the cerebrovasculature as well as neurons and glia. Nevertheless, the specific regulation and actions of brain- and vascular-derived IGF-1 is poorly understood. The diverse effects of IGF-1 discovered thus far reveal a complex endocrine and paracrine system essential for integrating many of the functions necessary for brain health. Identification of the mechanisms of IGF-1 actions will undoubtedly provide critical insight into regulation of brain function in general and the causes of cognitive decline with age.

Immune marker CD68 correlates with cognitive impairment in normally aged rats

The relationship between heightened neuroinflammation and cognitive decline in the normally aged brain is still debatable, as most data are derived from insult-related models. Accordingly, the aim of the current study was to determine whether a link could be established for 2 immune markers at the post-transcriptional level; CD68 and MHC-II, in a normally aged (24-month-old) rat population discriminated for their learning abilities. Using the Morris Water Maze (MWM) task, aged rats were divided into aged learning-impaired (AI) or -unimpaired (AU) groups. Western immunoblots of hippocampal tissue revealed a significant increase of CD68 in AI rats compared to the AU group. Moreover, up-regulated CD68 expression correlated with increased latency times in the MWM task. Immunofluorescence for CD68 revealed intense staining in the white matter regions and CA3 subregion of the hippocampus in the AI group. Despite expression of MHC-II in the AI group, no correlation was found. Overall, these data suggest that CD68 could play a role associated with cognitive decline in a subgroup of the normally aged population.