Aging causes morphological alterations in astrocytes and microglia in human substantia nigra pars compacta

Inhibiting Immune Crosstalk by Modulation of the Intracellular Function and Extracellular Environment of Diseased Microglia to Boost Parkinson's Disease Therapy

Microglia usually phagocytose excessive α-synuclein (α-syn) aggregates and turn into diseased analogues in Parkinson's disease (PD), which can present α-syn-associated antigens, secrete cytokines and chemokines to recruit peripheral immune cells, and form strong immune crosstalk to aggravate PD progression. Hence, targeting the diseased microglia and inhibiting their immune crosstalk emerge as promising strategies for PD therapy. Herein, we reprogram the diseased microglia to efficiently degrade α-syn aggregates and neutralize neuroinflammatory factors to reduce the detrimental immune crosstalk and enhance therapeutic efficacy using rationally designed core-shell IHM nanoparticles, which consist of a ligustilide-functionalized Cu2-xSe nanoparticle (CSL NP) core and a hybrid cell membrane shell. The CSL NPs can redress the diseased microglia to reduce over-presented antigens by dual roles of reducing microglial RAGE-mediated phagocytosis of α-syn aggregates and increasing the microglial mature cathepsin D (m-CTSD) to efficiently degrade α-syn aggregates. The hybrid cell membrane shell is formed by a MES23.5 cell membrane (MCM) and IFN-γ-treated RAW264.7 cell membrane (IRCM). It can not only target diseased microglia by the specific interactions between VCAM-1 on the MCM and α4β1 integrin on the microglial membrane but also absorb and reduce the secretion of neuroinflammatory factors by diseased microglia through upregulated neuroinflammatory cytokine receptors such as IL1R1, TNFR1, and CCR2 on the surface of IRCM. The biomimetic core-shell IHM nanoparticles can be effectively delivered into the brain via meningeal lymphatic vessels to modulate the diseased microglia for boosting PD therapy. Our study demonstrates the promise of targeting diseased microglia to reduce their immune crosstalk in the treatment of PD and other neurodegenerative diseases.

The Aging Substantia Nigra is Characterized by ROS Accumulation Potentially Resulting in Increased Neuroinflammation and Cytoskeletal Remodeling

Aging is a progressive and irreversible process, serving as the primary risk factor for neurodegenerative disorders. This study aims to identify the molecular mechanisms underlying physiological aging within the substantia nigra, which is primarily affected by Parkinson's disease, and to draw potential conclusions on the earliest events leading to neurodegeneration in this specific brain region. The characterization of essential stages in aging progress can enhance knowledge of the mechanisms that promote the development of Parkinson's disease. To gain a comprehensive overview three study groups are utilized: young individuals (mean age: 28.7 years), middle-aged (mean age: 62.3 years), and elderly individuals (mean age: 83.9 years). Using the proteomic approach, crucial features of physiological aging are able to be identified. These include heightened oxidative stress, enhanced lysosomal degradation, autophagy, remodeling of the cytoskeleton, changes in the structure of the mitochondria, alterations in vesicle transportation, and synaptic plasticity.

The crosstalk between CNS resident glial cells and peripheral immune cells is critical for age-dependent demyelination and subsequent remyelination

White-matter diseases like multiple sclerosis begin in young adulthood. Aging, being a risk factor, contributes to the progression of these diseases and makes neurological disabilities worsen. Aging causes white matter alteration due to myelin loss, axonal degeneration, and hyperintensities, resulting in cognitive impairment and neurological disorders. Aging also negatively affects central nervous system resident glial cells and peripheral immune cells, contributing to myelin degeneration and diminished myelin renewal process. Restoration of myelin failure with aging accelerates the progression of cognitive decline. This review will mainly focus on how age-related altered functions of glial and peripheral cells will affect myelin sheath alteration and myelin restoration. This understanding can give us insights into the underlying mechanisms of demyelination and failure of remyelination with aging concerning altered glial and peripheral immune cell function and their crosstalk. Also, we will explain the therapeutic strategies to enhance the remyelination process of an aging brain to improve the cognitive health of an aging person.

Crosstalk between neuroinflammation and ferroptosis: Implications for Parkinson's disease progression

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the degeneration of dopaminergic neurons and the aggregation of α-synuclein. Neuroinflammation is triggered by the activation of microglia and astrocytes, which release pro-inflammatory factors that exacerbate neuronal damage. This inflammatory state also disrupts iron homeostasis, leading to the occurrence of ferroptosis. Ferroptosis is characterized by lipid peroxidation of cell membranes and iron overload. Abnormal accumulation of iron in the brain increases oxidative stress and lipid peroxidation, further aggravating neuroinflammation and damage to dopaminergic neurons. Natural products have garnered attention for their antioxidant, anti-inflammatory, and neuroprotective properties, with many plant extracts showing promising therapeutic potential in PD research. This study further investigates the potential therapeutic roles of various natural products in regulating neuroinflammation and ferroptosis. The results suggest that natural products have significant therapeutic potential in modulating the interaction between neuroinflammation and ferroptosis, making them potential treatments for PD. Future research should further validate the safety and efficacy of these natural compounds in clinical applications to develop novel therapeutic strategies for PD.

Temporal Profiling of Male Cortical Astrocyte Transcription Predicts Molecular Shifts From Early Development to Aging

Astrocytes are the most abundant glial cell type in the central nervous system (CNS). Astrocytes are born during the early postnatal period in the rodent brain and mature alongside neurons, demonstrating remarkable morphological structural complexity, which is attained in the second postnatal month. Throughout this period of development and across the remainder of the lifespan, astrocytes participate in CNS homeostasis, support neuronal partners, and contribute to nearly all aspects of CNS function. In the present study, we analyzed astrocyte gene expression in the cortex of wild-type male rodents throughout their lifespan (postnatal 7 days to 18 months). A pairwise timepoint comparison of differential gene expression during early development and CNS maturation (7-60 days) revealed four unique astrocyte gene clusters, each with hundreds of genes, which demonstrate unique temporal profiles. These clusters are distinctively related to cell division, cell morphology, cellular communication, and vascular structure and regulation. A similar analysis across adulthood and in the aging brain (3 to 18 months) identified similar patterns of grouped gene expression related to cell metabolism and cell structure. Additionally, our analysis identified that during the aging process astrocytes demonstrate a bias toward shorter transcripts, with loss of longer genes related to synapse development and a significant increase in shorter transcripts related to immune regulation and the response to DNA damage. Our study highlights the critical role that astrocytes play in maintaining CNS function throughout life and reveals molecular shifts that occur during development and aging in the cortex of male mice.

Epigenetic regulation of iron metabolism and ferroptosis in Parkinson's disease: Identifying novel epigenetic targets

Parkinson's disease (PD) is a neurodegenerative disease, and emerging evidence has shown that iron deposition, ferroptosis and epigenetic modifications are implicated in the pathogenesis of PD. However, the interplay among these factors in PD has not been fully understood. In this review, we provide an overview of the current research progress on iron metabolism, ferroptosis and epigenetic alterations associated with PD. Furthermore, we present new frontiers concerning various epigenetic modifications related to iron metabolism and ferroptosis that might contribute to the pathology of PD. Notably, epigenetic modifications of iron metabolism and ferroptosis as both diagnostic and therapeutic targets in PD have been discussed. This opens new avenues for the regulation of iron homeostasis and ferroptosis in PD from epigenetic perspectives, and provides evidence for their potential implications in the diagnosis and treatment of PD.

Systemic Rejuvenating Interventions: Perspectives on Neuroinflammation and Blood-Brain Barrier Integrity

The aging process results in structural, functional, and immunological changes in the brain, which contribute to cognitive decline and increase vulnerability to neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and stroke-related complications. Aging leads to cognitive changes and also affect executive functions. Additionally, it causes neurogenic and neurochemical alterations, such as a decline in dopamine and acetylcholine levels, which also impact cognitive performance. The chronic inflammation caused by aging contributes to the impairment of the blood-brain barrier (BBB), contributing to the infiltration of immune cells and exacerbating neuronal damage. Therefore, rejuvenating therapies such as heterochronic parabiosis, cerebrospinal fluid (CSF) administration, plasma, platelet-rich plasma (PRP), and stem cell therapy have shown potential to reverse these changes, offering new perspectives in the treatment of age-related neurological diseases. This review focuses on highlighting the effects of rejuvenating interventions on neuroinflammation and the BBB.

Aging and MPTP Sensitivity Depend on Molecular and Ultrastructural Signatures of Astroglia and Microglia in Mice Substantia Nigra

Both astroglia and microglia show region-specific distribution in CNS and often maladapt to age-associated alterations within their niche. Studies on autopsied substantia nigra (SN) of Parkinson's disease (PD) patients and experimental models propose gliosis as a trigger for neuronal loss. Epidemiological studies propose an ethnic bias in PD prevalence, since Caucasians are more susceptible than non-whites. Similarly, different mice strains are variably sensitive to MPTP. We had earlier likened divergent MPTP sensitivity of C57BL/6 J and CD-1 mice with differential susceptibility to PD, based on the numbers of SN neurons. We examined whether the variability was incumbent to inter-strain differences in glial features of male C57BL/6 J and CD-1 mice. Stereological counts showed relatively more microglia and fewer astrocytes in the SN of normal C57BL/6 J mice, suggesting persistence of an immune-vigilant state. MPTP-induced microgliosis and astrogliosis in both strains suggest their involvement in pathogenesis. ELISA of pro-inflammatory cytokines in the ventral-midbrain revealed augmentation of TNF-α and IL-6 at middle age in both strains that reduced at old age, suggesting middle age as a critical, inflamm-aging-associated time point. TNF-α levels were high in C57BL/6 J, through aging and post-MPTP, while IL-6 and IL-1β were upregulated at old age. CD-1 had higher levels of anti-inflammatory cytokine TGF-β. MPTP challenge caused upregulation of enzymes MAO-A, MAO-B, and iNOS in both strains. Post-MPTP enhancement in fractalkine and hemeoxygenase-1 may be neuron-associated compensatory signals. Ultrastructural observations of elongated astroglial/microglial mitochondria vis-à-vis the shrunken ones in neurons suggest a scale-up of their functions with neurotoxic consequences. Thus, astroglia and microglia may modulate aging and PD susceptibility.

Adolescent Alcohol and the Spectrum of Cognitive Dysfunction in Aging

Among the many changes associated with aging, inflammation in the central nervous system (CNS) and throughout the body likely contributes to the constellation of health-related maladies associated with aging. Genetics, lifestyle factors, and environmental experiences shape the trajectory of aging-associated inflammation, including the developmental timing, frequency, and intensity of alcohol consumption. This chapter posits that neuroinflammatory processes form a critical link between alcohol exposure and the trajectory of healthy aging, at least in part through direct or indirect interactions with cholinergic circuits that are crucial to cognitive integrity. In this chapter, we begin with a discussion of how inflammation changes from early development through late aging; discuss the role of inflammation and alcohol in the emergence of mild cognitive impairment (MCI); elaborate on critical findings on the contribution of alcohol-related thiamine deficiency to the loss of cholinergic function and subsequent development of Wernicke-Korsakoff syndrome (WKS); and present emerging findings at the intersection of alcohol and Alzheimer's disease and related dementias (ADRD). In doing so, our analysis points toward inflammation-mediated compromise of basal forebrain cholinergic function as a key culprit in cognitive dysfunction associated with chronic alcohol exposure, effects that may be rescuable through either pharmacological or behavioral approaches. Furthermore, our chapter reveals an interesting dichotomy in the effects of alcohol on neuropathological markers of ADRD that depend upon both biological sex and genetic vulnerability.

Neuroglia in aging

Aging is associated with morphologic and functional decline of the brain active milieu and, in particular, of the neuroglia, which compromises homeostatic support and neuroprotection. Astrocytes in aging undergo complex and region specific changes, manifested by morphologic atrophy and widespread functional asthenia. Aging leads to mitochondrial malfunction and reduced protein/lipid ratio in human astrocytes. Oligodendrocyte lineage cells are the most affected cells by the aging process, which limits myelinating capacity, thus leading to a substantial reduction in the white matter and deficient brain connectome. Finally, microglia undergo a morphologic functional dystrophy in the aged human brain which curtails brain defenses and increases brain vulnerability to neuropathology and especially to age-dependent neurodegenerative disorders. Lifestyle modifications, such as enriched environment, physical exercise, and healthy dieting, boost neuroglial support, thus improving cognitive longevity.

Combination antiretroviral therapy prevents SIV- induced aging in the hippocampus and neurodegeneration throughout the brain

Virus-induced accelerated aging has been proposed as a potential mechanism underlying the persistence of HIV-associated neurocognitive disorders (HAND) despite advances in access and adherence to combination antiretroviral therapies (cART). While some studies have demonstrated evidence of accelerated aging in PLWH, studies examining acute infection, and cART intervention are limited, with most studies being in vitro or utilizing small animal models. Here, we utilized FFPE tissues from Simian immunodeficiency virus (SIV) infected rhesus macaques to assess the levels of two proteins commonly associated with aging - the cellular senescence marker p16INK4a (p16) and the NAD-dependent deacetylase sirtuin 1 (SIRT1). Our central hypothesis was that SIV infection induces accelerated aging phenotypes in the brain characterized by increased expression of p16 and altered expression of SIRT1 that correlate with increased neurodegeneration, and that cART inhibits this process. We found that SIV infection induced increased GFAP, p16, SIRT1, and neurodegeneration in multiple brain regions, and treatment with cART reduced GFAP expression in SIV-infected animals and thus likely decreases inflammation in the brain. Importantly, cART reversed SIV-induced accelerated aging (p16 and SIRT1) and neurodegeneration in the frontal lobe and hippocampus. Combined, these data suggest that cART is both safe and effective in reducing neuroinflammation and age-associated alterations in astrocytes that contribute to neurodegeneration, providing possible therapeutic targets in the treatment of HAND.

Region-specific and age-related differences in astrocytes in the human brain

Astrocyte heterogeneity and its relation to aging in the normal human brain remain poorly understood. We here analyzed astrocytes in gray and white matter brain tissues obtained from donors ranging in age between the neonatal period to over 100 years. We show that astrocytes are differently distributed with higher density in the white matter. This regional difference in cellular density becomes less prominent with age. Additionally, we confirm the presence of morphologically distinct astrocytes, with gray matter astrocytes being morphologically more complex. Notably, gray matter astrocytes morphologically change with age, while white matter astrocytes remain relatively consistent in morphology. Using regional mass spectrometry-based proteomics, we did, however, identify astrocyte specific proteins with regional differences in abundance, reflecting variation in cellular density or expression level. Importantly, the expression of some astrocyte specific proteins region-dependently decreases with age. Taken together, we provide insights into region- and age-related differences in astrocytes in the human brain.

Nanomaterials as Microglia Modulators in the Treatment of Central Nervous System Disorders

Microglia play a pivotal role in the central nervous system (CNS) homeostasis, acting as housekeepers and defenders of the surrounding environment. These cells can elicit their functions by shifting into two main phenotypes: pro-inflammatory classical phenotype, M1, and anti-inflammatory alternative phenotype, M2. Despite their pivotal role in CNS homeostasis, microglia phenotypes can influence the development and progression of several CNS disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, ischemic stroke, traumatic brain injuries, and even brain cancer. It is thus clear that the possibility of modulating microglia activation has gained attention as a therapeutic tool against many CNS pathologies. Nanomaterials are an unprecedented tool for manipulating microglia responses, in particular, to specifically target microglia and elicit an in situ immunomodulation activity. This review focuses the discussion on two main aspects: analyzing the possibility of using nanomaterials to stimulate a pro-inflammatory response of microglia against brain cancer and introducing nanostructures able to foster an anti-inflammatory response for treating neurodegenerative disorders. The final aim is to stimulate the analysis of the development of new microglia nano-immunomodulators, paving the way for innovative and effective therapeutic approaches for the treatment of CNS disorders.

Telomere shortening induces aging-associated phenotypes in hiPSC-derived neurons and astrocytes

Telomere shortening is a well-established hallmark of cellular aging. Telomerase reverse transcriptase (TERT) plays a crucial role in maintaining the length of telomeres, which are specialised protective caps at the end of chromosomes. The lack of in vitro aging models, particularly for the central nervous system (CNS), has impeded progress in understanding aging and age-associated neurodegenerative diseases. In this study, we aimed to explore the possibility of inducing aging-associated features in cell types of the CNS using hiPSC (human induced pluripotent stem cell) technology. To achieve this, we utilised CRISPR/Cas9 to generate hiPSCs with a loss of telomerase function and shortened telomeres. Through directed differentiation, we generated motor neurons and astrocytes to investigate whether telomere shortening could lead to age-associated phenotypes. Our findings revealed that shortened telomeres induced age-associated characteristics in both motor neurons and astrocytes including increased cellular senescence, heightened inflammation, and elevated DNA damage. We also observed cell-type specific age-related morphology changes. Additionally, our study highlighted the fundamental role of TERT and telomere shortening in neural progenitor cell (NPC) proliferation and neuronal differentiation. This study serves as a proof of concept that telomere shortening can effectively induce aging-associated phenotypes, thereby providing a valuable tool to investigate age-related decline and neurodegenerative diseases.

Fecal Microbiota Transplantation from Aged Mice Render Recipient Mice Resistant to MPTP-Induced Nigrostriatal Degeneration Via a Neurogenesis-Dependent but Inflammation-Independent Manner

Accumulating data support a crucial role of gut microbiota in Parkinson's disease (PD). However, gut microbiota vary with age and, thus, will affect PD in an age-dependent, but unknown manner. We examined the effects of fecal microbiota transplantation (FMT) pretreatment, using fecal microbiota from young (7 weeks) or aged mice (23 months), on MPTP-induced PD model. Motor function, pathological changes, striatal neurotransmitters, neuroinflammation, gut inflammation and gut permeability were examined. Gut microbiota composition and metabolites, namely short-chain fatty acids (SCFAs), were analyzed. Neurogenesis was also evaluated by measuring the number of doublecortin-positive (DCX+) neurons and Ki67-positive (Ki67+) cells in the hippocampus. Expression of Cd133 mRNA, a cellular stemness marker, in the hippocampus was also examined. Mice who received FMT from young mice showed MPTP-induced motor dysfunction, and reduction of striatal dopamine (DA), dopaminergic neurons and striatal tyrosine hydroxylase (TH) levels. Interestingly and unexpectedly, mice that received FMT from aged mice showed recovery of motor function and rescue of dopaminergic neurons and striatal 5-hydroxytryptamine (5-HT), as well as decreased DA metabolism after MPTP challenge. Further, they showed improved metabolic profiling and a decreased amount of fecal SCFAs. High-throughput sequencing revealed that FMT remarkably reshaped the gut microbiota of recipient mice. For instance, levels of genus Akkermansia and Candidatus Saccharimonas were elevated in fecal samples of recipient mice receiving aged microbiota (AM + MPTP mice) than YM + MPTP mice. Intriguingly, both young microbiota and aged microbiota had no effect on neuroinflammation, gut inflammation or gut permeability. Notably, AM + MPTP mice showed a marked increase in DCX+ neurons, as well as Ki67+ cells and Cd133 expression in the hippocampal dentate gyrus (DG) compared to YM + MPTP mice. These results suggest that FMT from aged mice augments neurogenesis, improves motor function and restores dopaminergic neurons and neurotransmitters in PD model mice, possibly through increasing neurogenesis.

Astrocytes in the Optic Nerve Are Heterogeneous in Their Reactivity to Glaucomatous Injury

The optic nerve head is thought to be the site of initial injury to retinal ganglion cell injury in glaucoma. In the initial segment of the optic nerve directly behind the globe, the ganglion cell axons are unmyelinated and come into direct contact to astrocytes, suggesting that astrocytes may play a role in the pathology of glaucoma. As in other parts of the CNS, optic nerve head astrocytes respond to injury by characteristic changes in cell morphology and gene expression profile. Using RNA-sequencing of glaucomatous optic nerve heads, single-cell PCR, and an in-vivo assay, we demonstrate that an up-regulation of astrocytic phagocytosis is an early event after the onset of increased intraocular pressure. We also show that astrocytes in the glial lamina of the optic nerve are apparently functionally heterogeneous. At any time, even in naïve nerves, some of the cells show signs of reactivity-process hypertrophy, high phagocytic activity, and expression of genetic markers of reactivity whereas neighboring cells apparently are inactive. A period of increased intraocular pressure moves more astrocytes towards the reactive phenotype; however, some cells remain unreactive even in glaucomatous nerves.

Brain-Biomarker Changes in Body Fluids of Patients with Parkinson's Disease

Parkinson's disease (PD) is an incurable neurodegenerative disease that is rarely diagnosed at an early stage. Although the understanding of PD-related mechanisms has greatly improved over the last decade, the diagnosis of PD is still based on neurological examination through the identification of motor symptoms, including bradykinesia, rigidity, postural instability, and resting tremor. The early phase of PD is characterized by subtle symptoms with a misdiagnosis rate of approximately 16-20%. The difficulty in recognizing early PD has implications for the potential use of novel therapeutic approaches. For this reason, it is important to discover PD brain biomarkers that can indicate early dopaminergic dysfunction through their changes in body fluids, such as saliva, urine, blood, or cerebrospinal fluid (CSF). For the CFS-based test, the invasiveness of sampling is a major limitation, whereas the other body fluids are easier to obtain and could also allow population screening. Following the identification of the crucial role of alpha-synuclein (α-syn) in the pathology of PD, a very large number of studies have summarized its changes in body fluids. However, methodological problems have led to the poor diagnostic/prognostic value of this protein and alternative biomarkers are currently being investigated. The aim of this paper is therefore to summarize studies on protein biomarkers that are alternatives to α-syn, particularly those that change in nigrostriatal areas and in biofluids, with a focus on blood, and, eventually, saliva and urine.

Apoptotic Factors and Mitochondrial Complexes Assist Determination of Strain-Specific Susceptibility of Mice to Parkinsonian Neurotoxin MPTP

Identification of genetic mutations in Parkinson's disease (PD) promulgates the genetic nature of disease susceptibility. Resilience-associated genes being unknown till date, the normal genetic makeup of an individual may be determinative too. Our earlier studies comparing the substantia nigra (SN) and striatum of C57BL/6J, CD-1 mice, and their F1-crossbreds demonstrated the neuroprotective role of admixing against the neurotoxin MPTP. Furthermore, the differences in levels of mitochondrial fission/fusion proteins in the SN of parent strains imply effects on mitochondrial biogenesis. Our present investigations suggest that the baseline levels of apoptotic factors Bcl-2, Bax, and AIF differ across the three strains and are differentially altered in SN following MPTP administration. The reduction in complex-I levels exclusively in MPTP-injected C57BL/6J reiterates mitochondrial involvement in PD pathogenesis. The MPTP-induced increase in complex-IV, in the nigra of both parent strains, may be compensatory in nature. The ultrastructural evaluation showed fairly preserved mitochondria in the dopaminergic neurons of CD-1 and F1-crossbreds. However, in CD-1, the endoplasmic reticulum demonstrated distinct luminal enlargement, bordering onto ballooning, suggesting proteinopathy as a possible initial trigger.The increase in α-synuclein in the pars reticulata of crossbreds suggests a supportive role for this output nucleus in compensating for the lost function of pars compacta. Alternatively, since α-synuclein over-expression occurs in different brain regions in PD, the α-synuclein increase here may suggest a similar pathogenic outcome. Further understanding is required to resolve this biological contraption. Nevertheless, admixing reduces the risk to MPTP by favoring anti-apoptotic consequences. Similar neuroprotection may be envisaged in the admixed populace of Anglo-Indians.

Robust differences in cortical cell type proportions across healthy human aging inferred through cross-dataset transcriptome analyses

Age-related declines in cognitive function are driven by cell type-specific changes in the brain. However, it remains challenging to study cellular differences associated with healthy aging as traditional approaches scale poorly to the sample sizes needed to capture aging and cellular heterogeneity. Here, we employed cellular deconvolution to estimate relative cell type proportions using frontal cortex bulk gene expression from individuals without psychiatric conditions or brain pathologies. Our analyses comprised 8 datasets and 6 cohorts (1142 subjects and 1429 samples) with ages of death spanning 15-90 years. We found aging associated with profound differences in cellular proportions, with the largest changes reflecting fewer somatostatin- and vasoactive intestinal peptide-expressing interneurons, more astrocytes and other non-neuronal cells, and a suggestive "U-shaped" quadratic relationship for microglia. Cell type associations with age were markedly robust across bulk-and single nucleus datasets. Altogether, we present a comprehensive account of proportional differences in cortical cell types associated with healthy aging.

Atrophic astrocytes in aged marmosets present tau hyperphosphorylation, RNA oxidation, and DNA fragmentation

Astrocytes perform multiple essential functions in the brain showing morphological changes. Hypertrophic astrocytes are commonly observed in cognitively healthy aged animals, implying a functional defense mechanism without losing neuronal support. In neurodegenerative diseases, astrocytes show morphological alterations, such as decreased process length and reduced number of branch points, known as astroglial atrophy, with detrimental effects on neuronal cells. The common marmoset (Callithrix jacchus) is a non-human primate that, with age, develops several features that resemble neurodegeneration. In this study, we characterize the morphological alterations in astrocytes of adolescent (mean 1.75 y), adult (mean 5.33 y), old (mean 11.25 y), and aged (mean 16.83 y) male marmosets. We observed a significantly reduced arborization in astrocytes of aged marmosets compared to younger animals in the hippocampus and entorhinal cortex. These astrocytes also show oxidative damage to RNA and increased nuclear plaques in the cortex and tau hyperphosphorylation (AT100). Astrocytes lacking S100A10 protein show a more severe atrophy and DNA fragmentation. Our results demonstrate the presence of atrophic astrocytes in the brains of aged marmosets.

Are cytoskeleton changes observed in astrocytes functionally linked to aging?

Astrocytes are active participants in the performance of the Central Nervous System (CNS) in both health and disease. During aging, astrocytes are susceptible to reactive astrogliosis, a molecular state characterized by functional changes in response to pathological situations, and cellular senescence, characterized by loss of cell division, apoptosis resistance, and gain of proinflammatory functions. This results in two different states of astrocytes, which can produce proinflammatory phenotypes with harmful consequences in chronic conditions. Reactive astrocytes and senescent astrocytes share morpho-functional features that are dependent on the organization of the cytoskeleton. However, such changes in the cytoskeleton have yet to receive the necessary attention to explain their role in the alterations of astrocytes that are associated with aging and pathologies. In this review, we summarize all the available findings that connect changes in the cytoskeleton of the astrocytes with aging. In addition, we discuss future avenues that we believe will guide such a novel topic.

The common marmoset as a model of neurodegeneration

Human life expectancy has increased over the past few centuries, and the incidence of dementia in the older population is also projected to continue to rise. Neurodegenerative diseases are complex multifactorial conditions for which no effective treatments are currently available. Animal models are necessary to understand the causes and progression of neurodegeneration. Nonhuman primates (NHPs) offer significant advantages for the study of neurodegenerative disease. Among them, the common marmoset, Callithrix jacchus, stands out due to its easy handling, complex brain architecture, and occurrence of spontaneous beta-amyloid (Aβ) and phosphorylated tau aggregates with aging. Furthermore, marmosets present physiological adaptations and metabolic alterations associated with the increased risk of dementia in humans. In this review, we discuss the current literature on the use of marmosets as a model of aging and neurodegeneration. We highlight aspects of marmoset physiology associated with aging, such as metabolic alterations, which may help understand their vulnerability to developing a neurodegenerative phenotype that goes beyond normal aging.

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.

Towards early detection of neurodegenerative diseases: A gut feeling

The gastrointestinal tract communicates with the nervous system through a bidirectional network of signaling pathways called the gut-brain axis, which consists of multiple connections, including the enteric nervous system, the vagus nerve, the immune system, endocrine signals, the microbiota, and its metabolites. Alteration of communications in the gut-brain axis is emerging as an overlooked cause of neuroinflammation. Neuroinflammation is a common feature of the pathogenic mechanisms involved in various neurodegenerative diseases (NDs) that are incurable and debilitating conditions resulting in progressive degeneration and death of neurons, such as in Alzheimer and Parkinson diseases. NDs are a leading cause of global death and disability, and the incidences are expected to increase in the following decades if prevention strategies and successful treatment remain elusive. To date, the etiology of NDs is unclear due to the complexity of the mechanisms of diseases involving genetic and environmental factors, including diet and microbiota. Emerging evidence suggests that changes in diet, alteration of the microbiota, and deregulation of metabolism in the intestinal epithelium influence the inflammatory status of the neurons linked to disease insurgence and progression. This review will describe the leading players of the so-called diet-microbiota-gut-brain (DMGB) axis in the context of NDs. We will report recent findings from studies in model organisms such as rodents and fruit flies that support the role of diets, commensals, and intestinal epithelial functions as an overlooked primary regulator of brain health. We will finish discussing the pivotal role of metabolisms of cellular organelles such as mitochondria and peroxisomes in maintaining the DMGB axis and how alteration of the latter can be used as early disease makers and novel therapeutic targets.

Novel Microglia-based Therapeutic Approaches to Neurodegenerative Disorders

As prominent immune cells in the central nervous system, microglia constantly monitor the environment and provide neuronal protection, which are important functions for maintaining brain homeostasis. In the diseased brain, microglia are crucial mediators of neuroinflammation that regulates a broad spectrum of cellular responses. In this review, we summarize current knowledge on the multifunctional contributions of microglia to homeostasis and their involvement in neurodegeneration. We further provide a comprehensive overview of therapeutic interventions targeting microglia in neurodegenerative diseases. Notably, we propose microglial depletion and subsequent repopulation as promising replacement therapy. Although microglial replacement therapy is still in its infancy, it will likely be a trend in the development of treatments for neurodegenerative diseases due to its versatility and selectivity.

An emerging role of astrocytes in aging/neuroinflammation and gut-brain axis with consequences on sleep and sleep disorders

Understanding the role of astrocytes in the central nervous system has changed dramatically over the last decade. The accumulating findings indicate that glial cells are involved not only in the maintenance of metabolic and ionic homeostasis and in the implementation of trophic functions but also in cognitive functions and information processing in the brain. Currently, there are some controversies regarding the role of astrocytes in complex processes such as aging of the nervous system and the pathogenesis of age-related neurodegenerative diseases. Many findings confirm the important functional role of astrocytes in age-related brain changes, including sleep disturbance and the development of neurodegenerative diseases and particularly Alzheimer's disease. Until recent years, neurobiological research has focused mainly on neuron-glial interactions, in which individual astrocytes locally modulate neuronal activity and communication between neurons. The review considers the role of astrocytes in the physiology of sleep and as an important "player" in the development of neurodegenerative diseases. In addition, the features of the astrocytic network reorganization during aging are discussed.

Glial aging and its impact on central nervous system myelin regeneration

Aging is a major risk factor for several neurodegenerative diseases and is associated with cognitive decline. In addition to affecting neuronal function, the aging process significantly affects the functional phenotype of the glial cell compartment, comprising oligodendrocyte lineage cells, astrocytes, and microglia. These changes result in a more inflammatory microenvironment, resulting in a condition that is favorable for neuron and synapse loss. In addition to facilitating neurodegeneration, the aging glial cell population has negative implications for central nervous system remyelination, a regenerative process that is of particular importance to the chronic demyelinating disease multiple sclerosis. This review will discuss the changes that occur with aging in the three main glial populations and provide an overview of the studies documenting the impact these changes have on remyelination.

Astrocytes in Ageing

Ageing is associated with a morphological and functional decline of astrocytes with a prevalence of morphological atrophy and loss of function. In particular, ageing is manifested by the shrinkage of astrocytic processes: branches and leaflets, which decreases synaptic coverage. Astrocytic dystrophy affects multiple functions astrocytes play in the brain active milieu. In particular, and in combination with an age-dependent decline in the expression of glutamate transporters, astrocytic atrophy translates into deficient glutamate clearance and K⁺ buffering. Decreased astrocyte presence may contribute to age-dependent remodelling of brain extracellular space, hence affecting extrasynaptic signalling. Old astrocytes lose endfeet polarisation of AQP4 water channels, thus limiting the operation of the glymphatic system. In ageing, astrocytes down-regulate their antioxidant capacity leading to decreased neuroprotection. All these changes may contribute to an age-dependent cognitive decline.

Contribution of Glial Cells to Polyglutamine Diseases: Observations from Patients and Mouse Models

Neurodegenerative diseases are broadly characterized neuropathologically by the degeneration of vulnerable neuronal cell types in a specific brain region. The degeneration of specific cell types has informed on the various phenotypes/clinical presentations in someone suffering from these diseases. Prominent neurodegeneration of specific neurons is seen in polyglutamine expansion diseases including Huntington's disease (HD) and spinocerebellar ataxias (SCA). The clinical manifestations observed in these diseases could be as varied as the abnormalities in motor function observed in those who have Huntington's disease (HD) as demonstrated by a chorea with substantial degeneration of striatal medium spiny neurons (MSNs) or those with various forms of spinocerebellar ataxia (SCA) with an ataxic motor presentation primarily due to degeneration of cerebellar Purkinje cells. Due to the very significant nature of the degeneration of MSNs in HD and Purkinje cells in SCAs, much of the research has centered around understanding the cell autonomous mechanisms dysregulated in these neuronal cell types. However, an increasing number of studies have revealed that dysfunction in non-neuronal glial cell types contributes to the pathogenesis of these diseases. Here we explore these non-neuronal glial cell types with a focus on how each may contribute to the pathogenesis of HD and SCA and the tools used to evaluate glial cells in the context of these diseases. Understanding the regulation of supportive and harmful phenotypes of glia in disease could lead to development of novel glia-focused neurotherapeutics.

The landscape of aging

Aging is characterized by a progressive deterioration of physiological integrity, leading to impaired functional ability and ultimately increased susceptibility to death. It is a major risk factor for chronic human diseases, including cardiovascular disease, diabetes, neurological degeneration, and cancer. Therefore, the growing emphasis on "healthy aging" raises a series of important questions in life and social sciences. In recent years, there has been unprecedented progress in aging research, particularly the discovery that the rate of aging is at least partly controlled by evolutionarily conserved genetic pathways and biological processes. In an attempt to bring full-fledged understanding to both the aging process and age-associated diseases, we review the descriptive, conceptual, and interventive aspects of the landscape of aging composed of a number of layers at the cellular, tissue, organ, organ system, and organismal levels.

Spatial profiles provide sensitive MRI measures of the midbrain micro- and macrostructure

The midbrain is the rostral-most part of the brainstem. It contains numerous nuclei and white matter tracts, which are involved in motor, auditory and visual processing, and changes in their structure and function have been associated with aging, as well as neurodegenerative disorders. Current tools for estimating midbrain subregions and their structure with MRI require high resolution and multi-parametric quantitative MRI measures. We propose an approach that relies on morphology to calculate profiles along the midbrain and show these profiles are sensitive to the underlying macrostructure of the midbrain. First, we show that the midbrain structure can be sampled, within subject space, along three main axes of the left and right midbrain, producing profiles that are similar across subjects. We use two data sets with different field strengths, that contain R1, R2* and QSM maps and show that the profiles are highly correlated both across subjects and between datasets. Next, we compare profiles of the midbrain that sample ROIs, and show that the profiles along the first two axes sample the midbrain in a way that reliably separates the main structures, i.e., the substantia nigra, the red nucleus, and periaqueductal gray. We further show that age differences which are localized to specific nuclei, are reflected in the profiles. Finally, we generalize the same approach to calculate midbrain profiles on a third clinically relevant dataset using HCP subjects, with metrics such as the diffusion tensor and semi-quantitative data such as T1w/T2w maps. Our results suggest that midbrain profiles, both of quantitative and semi-quantitative estimates are sensitive to the underlying macrostructure of the midbrain. The midbrain profiles are calculated in native space, and rely on simple measurements. We show that it is robust and can be easily expanded to different datasets, and as such we hope that it will be of great use to the community and to the study of the midbrain in particular.

Effects of long-term resveratrol treatment in hypothalamic astrocyte cultures from aged rats

Aging is intrinsically related to metabolic changes and characterized by the accumulation of oxidative and inflammatory damage, as well as alterations in gene expression and activity of several signaling pathways, which in turn impact on homeostatic responses of the body. Hypothalamus is a brain region most related to these responses, and increasing evidence has highlighted a critical role of astrocytes in hypothalamic homeostatic functions, particularly during aging process. The purpose of this study was to investigate the in vitro effects of a chronic treatment with resveratrol (1 µM during 15 days, which was replaced once every 3 days), a recognized anti-inflammatory and antioxidant molecule, in primary hypothalamic astrocyte cultures obtained from aged rats (24 months old). We observed that aging process changes metabolic, oxidative, inflammatory, and senescence parameters, as well as glial markers, while long-term resveratrol treatment prevented these effects. In addition, resveratrol upregulated key signaling pathways associated with cellular homeostasis, including adenosine receptors, nuclear factor erythroid-derived 2-like 2 (Nrf2), heme oxygenase 1 (HO-1), sirtuin 1 (SIRT1), proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), and phosphoinositide 3-kinase (PI3K). Our data corroborate the glioprotective effect of resveratrol in aged hypothalamic astrocytes, reinforcing the beneficial role of resveratrol in the aging process.

Second-generation antipsychotic olanzapine attenuates behavioral and prefrontal cortex synaptic plasticity deficits in a neurodevelopmental schizophrenia-related rat model

Second-generation antipsychotics are the drugs of choice for the treatment of neurodevelopmental-related mental diseases such as schizophrenia. Despite the effectiveness of these drugs to ameliorate some of the symptoms of schizophrenia, specifically the positive ones, the mechanisms beyond their antipsychotic effect are still poorly understood. Specifically, second-generation antipsychotics are reported to have anti-inflammatory, antioxidant and neuroplastic properties. Using the neonatal ventral hippocampus lesion (nVHL) in the rat, an accepted schizophrenia-related model, we evaluated the effect of the second-generation antipsychotic olanzapine (OLZ) in the behavioral, neuroplastic, and neuroinflammatory alterations exhibited in the nVHL animals. OLZ corrected the hyperlocomotion and impaired working memory of the nVHL animals but failed to enhance social disturbances of these animals. In the prefrontal cortex (PFC), OLZ restored the pyramidal cell structural plasticity in the nVHL rats, enhancing the dendritic arbor length, the spinogenesis and the proportion of mature spines. Moreover, OLZ attenuated astrogliosis as well as some pro-inflammatory, oxidative stress, and apoptosis-related molecules in the PFC. These findings reinforce the evidence of anti-inflammatory, antioxidant, and neurotrophic mechanisms of second-generation antipsychotics in the nVHL schizophrenia-related model, which allows for the possibility of developing more specific drugs for this disorder and thus avoiding the side effects of current schizophrenia treatments.

Prolonged, Low-Level Exposure to the Marine Toxin, Domoic Acid, and Measures of Neurotoxicity in Nonhuman Primates

BACKGROUND

The excitotoxic molecule, domoic acid (DA), is a marine algal toxin known to induce overt hippocampal neurotoxicity. Recent experimental and epidemiological studies suggest adverse neurological effects at exposure levels near the current regulatory limit (20 ppm, ∼0.075-0.1mg/kg). At these levels, cognitive effects occur in the absence of acute symptoms or evidence of neuronal death.

OBJECTIVES

This study aimed to identify adverse effects on the nervous system from prolonged, dietary DA exposure in adult, female Macaca fascicularis monkeys.

METHODS

Monkeys were orally exposed to 0, 0.075, and 0.15mg/kg per day for an average of 14 months. Clinical blood counts, chemistry, and cytokine levels were analyzed in the blood. In-life magnetic resonance (MR) imaging assessed volumetric and tractography differences in and between the hippocampus and thalamus. Histology of neurons and glia in the fornix, fimbria, internal capsule, thalamus, and hippocampus was evaluated. Hippocampal RNA sequencing was used to identify differentially expressed genes. Enrichment of gene networks for neuronal health, excitotoxicity, inflammation/glia, and myelin were assessed with Gene Set Enrichment Analysis.

RESULTS

Clinical blood counts, chemistry, and cytokine levels were not altered with DA exposure in nonhuman primates. Transcriptome analysis of the hippocampus yielded 748 differentially expressed genes (fold change≥1.5; p≤0.05), reflecting differences in a broad molecular profile of intermediate early genes (e.g., FOS, EGR) and genes related to myelin networks in DA animals. Between exposed and control animals, MR imaging showed comparable connectivity of the hippocampus and thalamus and histology showed no evidence of hypomyelination. Histological examination of the thalamus showed a larger microglia soma size and an extension of cell processes, but suggestions of a GFAP+astrocyte response showed no indication of astrocyte hypertrophy.

DISCUSSION

In the absence of overt hippocampal excitotoxicity, chronic exposure of Macaca fascicularis monkeys to environmentally relevant levels of DA suggested a subtle shift in the molecular profile of the hippocampus and the microglia phenotype in the thalamus that was possibly reflective of an adaptive response due to prolonged DA exposure. https://doi.org/10.1289/EHP10923.

Effect of senescence on the tyrosine hydroxylase and S100B immunoreactivity in the nigrostriatal pathway of the rat

Senescence is a natural and progressive physiological event that leads to a series of morphophysiological alterations in the organism. The brain is the most vulnerable organ to both structural and functional changes during this process. Dopamine is a key neurotransmitter for the proper functioning of the brain, directly involved in circuitries related with emotions, learning, motivation and reward. One of the main dopamine- producing nuclei is the substantia nigra pars compacta (SNpc), which establish connections with the striatum forming the so-called nigrostriatal pathway. S100B is a calcium binding protein mainly expressed by astrocytes, involved in both intracellular and extracellular processes, and whose expression is increased following injury in the nervous tissue, being a useful marker in altered status of central nervous system. The present study aimed to analyze the impact of senescence on the cells immunoreactive for tyrosine hydroxylase (TH) and S100B along the nigrostriatal pathway of the rat. Our results show an decreased expression of S100B⁺ cells in SNpc. In addition, there was a significant decrease in TH immunoreactivity in both projection fibers and TH⁺ cell bodies. In the striatum, a decrease in TH immunoreactivity was also observed, as well as an enlargement of the white matter bundles. Our findings point out that senescence is related to the anatomical and neurochemical changes observed throughout the nigrostriatal pathway.

Astrocyte plasticity in mice ensures continued endfoot coverage of cerebral blood vessels following injury and declines with age

Astrocytes extend endfeet that enwrap the vasculature, and disruptions to this association which may occur in disease coincide with breaches in blood-brain barrier (BBB) integrity. Here we investigate if focal ablation of astrocytes is sufficient to disrupt the BBB in mice. Targeted two-photon chemical apoptotic ablation of astrocytes induced a plasticity response whereby surrounding astrocytes extended processes to cover vascular vacancies. In young animals, replacement processes occur in advance of endfoot retraction, but this is delayed in aged animals. Stimulation of replacement astrocytes results in constriction of pre-capillary arterioles, suggesting that replacement astrocytes are functional. Pharmacological inhibition of pSTAT3, as well as astrocyte specific deletion of pSTAT3, reduces astrocyte replacement post-ablation, without perturbations to BBB integrity. Similar endfoot replacement occurs following astrocyte cell death due to reperfusion in a stroke model. Together, these studies uncover the ability of astrocytes to maintain cerebrovascular coverage via substitution from nearby cells.

Differences in Neuronal Numbers, Morphology, and Developmental Apoptosis in Mice Nigra Provide Experimental Evidence of Ontogenic Origin of Vulnerability to Parkinson's Disease

Parkinson disease (PD) prevalence varies by ethnicity. In an earlier study, we replicated the reduced vulnerability to PD in an admixed population, using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-susceptible C57BL/6 J, MPTP-resistant CD-1 and their F1 crossbreds. In the present study, we investigated if the differences have a developmental origin. Substantia nigra was evaluated at postnatal days 2 (P2), P6, P10, P14, P18, and P22. C57BL/6 J mice had smaller nigra and fewer dopaminergic neurons than the CD-1 and crossbreds at P2, which persisted through development. A significant increase in numbers and nigral volume was observed across strains until P14. A drastic decline thereafter was specific to C57BL/6 J. CD-1 and crossbreds retained their numbers from P14 to stabilize with supernumerary neurons at adulthood. The neuronal size increased gradually to attain adult morphology at P10 in the resistant strains, vis-à-vis at P22 in C57BL/6 J. Accordingly, in comparison to C57BL/6 J, the nigra of CD-1 and reciprocal crossbreds possessed cytomorphological features of resilience, since birth. The considerably lesser dopaminergic neuronal loss in the CD-1 and crossbreds was seen at P2 and P14 and thereafter was complemented by attenuated developmental cell death. The differences in programmed cell death were confirmed by reduced TUNEL labelling, AIF, and caspase-3 expression. GDNF expression aligned with the cell death pattern at P2 and P14 in both nigra and striatum. Earlier maturity of nigra and its neurons appears to be better features that reflect as MPTP resistance at adulthood. Thus, variable MPTP vulnerability in mice and also differential susceptibility to PD in humans may arise early during nigral development.

Gliotoxicity and Glioprotection: the Dual Role of Glial Cells

Glial cells (astrocytes, oligodendrocytes and microglia) are critical for the central nervous system (CNS) in both physiological and pathological conditions. With this in mind, several studies have indicated that glial cells play key roles in the development and progression of CNS diseases. In this sense, gliotoxicity can be referred as the cellular, molecular, and neurochemical changes that can mediate toxic effects or ultimately lead to impairment of the ability of glial cells to protect neurons and/or other glial cells. On the other hand, glioprotection is associated with specific responses of glial cells, by which they can protect themselves as well as neurons, resulting in an overall improvement of the CNS functioning. In addition, gliotoxic events, including metabolic stresses, inflammation, excitotoxicity, and oxidative stress, as well as their related mechanisms, are strongly associated with the pathogenesis of neurological, psychiatric and infectious diseases. However, glioprotective molecules can prevent or improve these glial dysfunctions, representing glial cells-targeting therapies. Therefore, this review will provide a brief summary of types and functions of glial cells and point out cellular and molecular mechanisms associated with gliotoxicity and glioprotection, potential glioprotective molecules and their mechanisms, as well as gliotherapy. In summary, we expect to address the relevance of gliotoxicity and glioprotection in the CNS homeostasis and diseases.

Replenishing the Aged Brains: Targeting Oligodendrocytes and Myelination?

Aging affects almost all the aspects of brain functions, but the mechanisms remain largely undefined. Increasing number of literatures have manifested the important role of glial cells in regulating the aging process. Oligodendroglial lineage cell is a major type of glia in central nervous system (CNS), composed of mature oligodendrocytes (OLs), and oligodendroglia precursor cells (OPCs). OLs produce myelin sheaths that insulate axons and provide metabolic support to meet the energy demand. OPCs maintain the population throughout lifetime with the abilities to proliferate and differentiate into OLs. Increasing evidence has shown that oligodendroglial cells display active dynamics in adult and aging CNS, which is extensively involved in age-related brain function decline in the elderly. In this review, we summarized present knowledge about dynamic changes of oligodendroglial lineage cells during normal aging and discussed their potential roles in age-related functional decline. Especially, focused on declined myelinogenesis during aging and underlying mechanisms. Clarifying those oligodendroglial changes and their effects on neurofunctional decline may provide new insights in understanding aging associated brain function declines.

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.

She Doesn't Even Go Here: The Role of Inflammatory Astrocytes in CNS Disorders

Astrocyte heterogeneity is a rapidly evolving field driven by innovative techniques. Inflammatory astrocytes, one of the first described subtypes of reactive astrocytes, are present in a variety of neurodegenerative diseases and may play a role in their pathogenesis. Moreover, genetic and therapeutic targeting of these astrocytes ameliorates disease in several models, providing support for advancing the development of astrocyte-specific disease modifying therapies. This review aims to explore the methods and challenges of identifying inflammatory astrocytes, the role these astrocytes play in neurological disorders, and future directions in the field of astrocyte heterogeneity.

The Role of Gut Microbiota and Gut-Brain Interplay in Selected Diseases of the Central Nervous System

The gut microbiome has attracted increasing attention from researchers in recent years. The microbiota can have a specific and complex cross-talk with the host, particularly with the central nervous system (CNS), creating the so-called “gut–brain axis”. Communication between the gut, intestinal microbiota, and the brain involves the secretion of various metabolites such as short-chain fatty acids (SCFAs), structural components of bacteria, and signaling molecules. Moreover, an imbalance in the gut microbiota composition modulates the immune system and function of tissue barriers such as the blood–brain barrier (BBB). Therefore, the aim of this literature review is to describe how the gut–brain interplay may contribute to the development of various neurological disorders, combining the fields of gastroenterology and neuroscience. We present recent findings concerning the effect of the altered microbiota on neurodegeneration and neuroinflammation, including Alzheimer’s and Parkinson’s diseases, as well as multiple sclerosis. Moreover, the impact of the pathological shift in the microbiome on selected neuropsychological disorders, i.e., major depressive disorders (MDD) and autism spectrum disorder (ASD), is also discussed. Future research on the effect of balanced gut microbiota composition on the gut–brain axis would help to identify new potential opportunities for therapeutic interventions in the presented diseases.

The Impact of IgA and the Microbiota on CNS Disease

Although anatomically distant from the central nervous system (CNS), gut-derived signals can dynamically regulate both peripheral immune cells and CNS-resident glial cells to modulate disease. Recent discoveries of specific microbial taxa and microbial derived metabolites that modulate neuroinflammation and neurodegeneration have provided mechanistic insight into how the gut may modulate the CNS. Furthermore, the participation of the gut in regulation of peripheral and CNS immune activity introduces a potential therapeutic target. This review addresses emerging literature on how the microbiome can affect glia and circulating lymphocytes in preclinical models of human CNS disease. Critically, this review also discusses how the host may in turn influence the microbiome, and how this may impact CNS homeostasis and disease, potentially through the production of IgA.

Changes in cytoplasmic and extracellular neuromelanin in human substantia nigra with normal aging

Neuromelanin (NM) is a dark polymer pigment produced in certain populations of catecholaminergic neurons in the brain. It is present in various areas of the human brain, most often in the substantia nigra (SN) pars compacta and the locus coeruleus, the main centers of dopaminergic and noradrenergic innervation, respectively. Interest in NM has revived in recent years due to the alleged link between NM and the particular vulnerability of NM-containing neurons to neurodegeneration. The aim of this work was to study the structural, cytochemical, and localization features of cytoplasmic and extracellular NM (eNM) in the human SN pars compacta during normal aging. Sections of human SN from young/middle-aged adults (25 to 51 years old, n=7) and older adults (60 to 78 years old, n=5), all of which had no neurological disorders, were stained histochemically for metals (Perls’ reaction, Mayer's hematoxylin) and immunohistochemically for tyrosine hydroxylase (TH), Iba- 1, and CD68. It was shown that dopaminergic neurons in SN pars compacta differ in the amount of NM and the intensity of TH-immunoreactivity. The number of NM-containing neurons with decreased TH-immunoreactivity positively correlates with age. eNM is present in SN pars compacta in both young/middle-aged and older adults. The number of eNM accumulations increases with aging. Cytoplasmic and eNM are predominantly not stained using histochemical methods for detecting metals in people of all ages. We did not detect the appearance of amoeboid microglia in human SN pars compacta with aging, but we found an age-related increase in microglial phagocytic activity. The absence of pronounced microgliosis, as well as a pronounced loss of NM-containing neurons, indicate the absence of neuroinflammation in human SN pars compacta during normal aging.

Modulation of Glial Function in Health, Aging, and Neurodegenerative Disease

In the central nervous system (CNS), glial cells, such as microglia and astrocytes, are normally associated with support roles including contributions to energy metabolism, synaptic plasticity, and ion homeostasis. In addition to providing support for neurons, microglia and astrocytes function as the resident immune cells in the brain. The glial function is impacted by multiple aspects including aging and local CNS changes caused by neurodegeneration. During aging, microglia and astrocytes display alterations in their homeostatic functions. For example, aged microglia and astrocytes exhibit impairments in the lysosome and mitochondrial function as well as in their regulation of synaptic plasticity. Recent evidence suggests that glia can also alter the pathology associated with many neurodegenerative disorders including Alzheimer's disease (AD) and Parkinson's disease (PD). Shifts in the microbiome can impact glial function as well. Disruptions in the microbiome can lead to aberrant microglial and astrocytic reactivity, which can contribute to an exacerbation of disease and neuronal dysfunction. In this review, we will discuss the normal physiological functions of microglia and astrocytes, summarize novel findings highlighting the role of glia in aging and neurodegenerative diseases, and examine the contribution of microglia and astrocytes to disease progression.

Glial cells and adaptive immunity in frontotemporal dementia with tau pathology

Neuroinflammation is involved in the aetiology of many neurodegenerative disorders including Alzheimer's disease, Parkinson's disease and motor neuron disease. Whether neuroinflammation also plays an important role in the pathophysiology of frontotemporal dementia is less well known. Frontotemporal dementia is a heterogeneous classification that covers many subtypes, with the main pathology known as frontotemporal lobar degeneration. The disease can be categorized with respect to the identity of the protein that causes the frontotemporal lobar degeneration in the brain. The most common subgroup describes diseases caused by frontotemporal lobar degeneration associated with tau aggregation, also known as primary tauopathies. Evidence suggests that neuroinflammation may play a role in primary tauopathies with genome-wide association studies finding enrichment of genetic variants associated with specific inflammation-related gene loci. These loci are related to both the innate immune system, including brain resident microglia, and the adaptive immune system through possible peripheral T-cell involvement. This review discusses the genetic evidence and relates it to findings in animal models expressing pathogenic tau as well as to post-mortem and PET studies in human disease. Across experimental paradigms, there seems to be a consensus regarding the involvement of innate immunity in primary tauopathies, with increased microglia and astrocyte density and/or activation, as well as increases in pro-inflammatory markers. Whilst it is less clear as to whether inflammation precedes tau aggregation or vice versa; there is strong evidence to support a microglial contribution to the propagation of hyperphosphorylated in tau frontotemporal lobar degeneration associated with tau aggregation. Experimental evidence-albeit limited-also corroborates genetic data pointing to the involvement of cellular adaptive immunity in primary tauopathies. However, it is still unclear whether brain recruitment of peripheral immune cells is an aberrant result of pathological changes or a physiological aspect of the neuroinflammatory response to the tau pathology.

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.

The C-terminal fragment of the heavy chain of the tetanus toxin (Hc-TeTx) improves motor activity and neuronal morphology in the limbic system of aged mice

In the aging process, the brain presents biochemical and morphological alterations. The neurons of the limbic system show reduced size dendrites, in addition to the loss of dendritic spines. These disturbances trigger a decrease in motor and cognitive function. Likewise, it is reported that during aging, in the brain, there is a significant decrease in neurotrophic factors, which are essential in promoting the survival and plasticity of neurons. The carboxyl-terminal fragment of the heavy chain of the tetanus toxin (Hc-TeTx) acts similarly to neurotrophic factors, inducing neuroprotection in different models of neuronal damage. The aim here, was to evaluate the effect of Hc-TeTx on the motor processes of elderly mice (18 months old), and its impact on the dendritic morphology and density of dendritic spines of neurons in the limbic system. The morphological analysis in the dendrites was evaluated employing Golgi-Cox staining. Hc-TeTx was administered (0.5 mg/kg) intraperitoneally for three days in 18-month-old mice. Locomotor activity was evaluated in a novel environment 30 days after the last administration of Hc-TeTx. Mice treated with Hc-TeTx showed significant changes in their motor behavior, and an increased dendritic spine density of pyramidal neurons in layers 3 and 5 of the prefrontal cortex in the hippocampus, and medium spiny neurons of the nucleus accumbens (NAcc). In conclusion, the Hc-TeTx improves the plasticity of the brain regions of the limbic system of aged mice. Therefore, it is proposed as a pharmacological alternative to prevent or delay brain damage during aging.

Utility of manual fractional anisotropy measurements in the management of patients with Parkinson disease: a feasibility study with a 1.5-T magnetic resonance imaging system

Background

Diffusion tensor imaging has emerged as a promising tool for quantitative analysis of neuronal damage in Parkinson disease, with potential value for diagnostic and prognostic evaluation.

Purpose

The aim of this study was to examine Parkinson disease-associated alterations in specific brain regions revealed by diffusion tensor imaging and how such alterations correlate with clinical variables.

Material and Methods

Diffusion tensor imaging was performed on 42 Parkinson disease patients and 20 healthy controls with a 1.5-T scanner. Manual fractional anisotropy measurements were performed for the ventral, intermediate, and dorsal portions of the substantia nigra, as well as for the cerebral peduncles, putamen, thalamus, and supplementary motor area. The correlation analysis between these measurements and the clinical variables was performed using χ² variance and multiple linear regression.

Results

Compared to healthy controls, Parkinson disease patients had significantly reduced fractional anisotropy values in the substantia nigra (P < .05). Some fractional anisotropy measurements in the substantia nigra correlated inversely with duration of Parkinson disease and Parkinson disease severity scores. Reduced fractional anisotropy values in the substantia nigra were also correlated inversely with age variable. fractional anisotropy values obtained for the right and left putamen varied significantly between males and females in both groups.

Conclusion

Manual fractional anisotropy measurements in the substantia nigra were confirmed to be feasible with a 1.5-T scanner. Diffusion tensor imaging data can be used as a reliable biomarker of Parkinson disease that can be used to support diagnosis, prognosis, and progression/treatment monitoring.

Reactive astrocyte nomenclature, definitions, and future directions

Reactive astrocytes are astrocytes undergoing morphological, molecular, and functional remodeling in response to injury, disease, or infection of the CNS. Although this remodeling was first described over a century ago, uncertainties and controversies remain regarding the contribution of reactive astrocytes to CNS diseases, repair, and aging. It is also unclear whether fixed categories of reactive astrocytes exist and, if so, how to identify them. We point out the shortcomings of binary divisions of reactive astrocytes into good-vs-bad, neurotoxic-vs-neuroprotective or A1-vs-A2. We advocate, instead, that research on reactive astrocytes include assessment of multiple molecular and functional parameters-preferably in vivo-plus multivariate statistics and determination of impact on pathological hallmarks in relevant models. These guidelines may spur the discovery of astrocyte-based biomarkers as well as astrocyte-targeting therapies that abrogate detrimental actions of reactive astrocytes, potentiate their neuro- and glioprotective actions, and restore or augment their homeostatic, modulatory, and defensive functions.