Iron overload and antioxidative role of perivascular astrocytes in aceruloplasminemia

Trace metals and astrocytes physiology and pathophysiology

Several trace metals, including iron, copper, manganese and zinc are essential for normal function of the nervous system. Both deficiency and excessive accumulation of these metals trigger neuropathological developments. The central nervous system (CNS) is in possession of dedicated homeostatic system that removes, accumulates, stores and releases these metals to fulfil nervous tissue demand. This system is mainly associated with astrocytes that act as dynamic reservoirs for trace metals, these being a part of a global system of CNS ionostasis. Here we overview physiological and pathophysiological aspects of astrocyte-cantered trace metals regulation.

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.

Cerebral Iron Deposition in Neurodegeneration

Disruption of cerebral iron regulation appears to have a role in aging and in the pathogenesis of various neurodegenerative disorders. Possible unfavorable impacts of iron accumulation include reactive oxygen species generation, induction of ferroptosis, and acceleration of inflammatory changes. Whole-brain iron-sensitive magnetic resonance imaging (MRI) techniques allow the examination of macroscopic patterns of brain iron deposits in vivo, while modern analytical methods ex vivo enable the determination of metal-specific content inside individual cell-types, sometimes also within specific cellular compartments. The present review summarizes the whole brain, cellular, and subcellular patterns of iron accumulation in neurodegenerative diseases of genetic and sporadic origin. We also provide an update on mechanisms, biomarkers, and effects of brain iron accumulation in these disorders, focusing on recent publications. In Parkinson’s disease, Friedreich’s disease, and several disorders within the neurodegeneration with brain iron accumulation group, there is a focal siderosis, typically in regions with the most pronounced neuropathological changes. The second group of disorders including multiple sclerosis, Alzheimer’s disease, and amyotrophic lateral sclerosis shows iron accumulation in the globus pallidus, caudate, and putamen, and in specific cortical regions. Yet, other disorders such as aceruloplasminemia, neuroferritinopathy, or Wilson disease manifest with diffuse iron accumulation in the deep gray matter in a pattern comparable to or even more extensive than that observed during normal aging. On the microscopic level, brain iron deposits are present mostly in dystrophic microglia variably accompanied by iron-laden macrophages and in astrocytes, implicating a role of inflammatory changes and blood–brain barrier disturbance in iron accumulation. Options and potential benefits of iron reducing strategies in neurodegeneration are discussed. Future research investigating whether genetic predispositions play a role in brain Fe accumulation is necessary. If confirmed, the prevention of further brain Fe uptake in individuals at risk may be key for preventing neurodegenerative disorders.

Role of endolysosome function in iron metabolism and brain carcinogenesis

Iron, the most abundant metal in human brain, is an essential microelement that regulates numerous cellular mechanisms. Some key physiological roles of iron include oxidative phosphorylation and ATP production, embryonic neuronal development, formation of iron-sulfur clusters, and the regulation of enzymes involved in DNA synthesis and repair. Because of its physiological and pathological importance, iron homeostasis must be tightly regulated by balancing its uptake, transport, and storage. Endosomes and lysosomes (endolysosomes) are acidic organelles known to contain readily releasable stores of various cations including iron and other metals. Increased levels of ferrous (Fe2+) iron can generate reactive oxygen species (ROS) via Fenton chemistry reactions and these increases can damage mitochondria and genomic DNA as well as promote carcinogenesis. Accumulation of iron in the brain has been linked with aging, diet, disease, and cerebral hemorrhage. Further, deregulation of brain iron metabolism has been implicated in carcinogenesis and may be a contributing factor to the increased incidence of brain tumors around the world. Here, we provide insight into mechanisms by which iron accumulation in endolysosomes is altered by pH and lysosome membrane permeabilization. Such events generate excess ROS resulting in mitochondrial DNA damage, fission, and dysfunction, as well as DNA oxidative damage in the nucleus; all of which promote carcinogenesis. A better understanding of the roles that endolysosome iron plays in carcinogenesis may help better inform the development of strategic therapeutic options for cancer treatment and prevention.

Protective effects of curcumin against iron-induced toxicity

Iron is an essential element in cellular metabolism that participates in many biochemical reactions. Nevertheless, iron overload in the body is the cause of damage in some organs including liver, glands, brain, heart, gastrointestinal tract and lung. Iron chelation therapy could be considered as an effective approach for removing excess iron. Deferoxamine, deferiprone and deferasirox are three common iron chelators in clinical practice but cause several side effects. In this context, the use of curcumin, a dietary phytochemical derived from turmeric, as a natural and safe antioxidant with iron-chelating activity may be a useful strategy for the management of iron overload. This review focuses on the deleterious effect of iron accumulation in different organs of the body as well as the therapeutic potential of curcumin against iron-induced toxicity.

Overdosing on iron: Elevated iron and degenerative brain disorders

IMPACT STATEMENT

Brain degenerative disorders, which include some neurodevelopmental disorders and age-associated diseases, cause debilitating neurological deficits and are generally fatal. A large body of emerging evidence indicates that iron accumulation in neurons within specific regions of the brain plays an important role in the pathogenesis of many of these disorders. Iron homeostasis is a highly complex and incompletely understood process involving a large number of regulatory molecules. Our review provides a description of what is known about how iron is obtained by the body and brain and how defects in the homeostatic processes could contribute to the development of brain diseases, focusing on Alzheimer's disease and Parkinson's disease as well as four other disorders belonging to a class of inherited conditions referred to as neurodegeneration based on iron accumulation (NBIA) disorders. A description of potential therapeutic approaches being tested for each of these different disorders is provided.

Ceruloplasmin replacement therapy ameliorates neurological symptoms in a preclinical model of aceruloplasminemia

Aceruloplasminemia is a monogenic disease caused by mutations in the ceruloplasmin gene that result in loss of protein ferroxidase activity. Ceruloplasmin plays a role in iron homeostasis, and its activity impairment leads to iron accumulation in liver, pancreas, and brain. Iron deposition promotes diabetes, retinal degeneration, and progressive neurodegeneration. Current therapies mainly based on iron chelation, partially control systemic iron deposition but are ineffective on neurodegeneration. We investigated the potential of ceruloplasmin replacement therapy in reducing the neurological pathology in the ceruloplasmin-knockout (CpKO) mouse model of aceruloplasminemia. CpKO mice were intraperitoneal administered for 2 months with human ceruloplasmin that was able to enter the brain inducing replacement of the protein levels and rescue of ferroxidase activity. Ceruloplasmin-treated mice showed amelioration of motor incoordination that was associated with diminished loss of Purkinje neurons and reduced brain iron deposition, in particular in the choroid plexus. Computational analysis showed that ceruloplasmin-treated CpKO mice share a similar pattern with wild-type animals, highlighting the efficacy of the therapy. These data suggest that enzyme replacement therapy may be a promising strategy for the treatment of aceruloplasminemia.

General Pathophysiology of Astroglia

Astroglial cells are involved in most if not in all pathologies of the brain. These cells can change the morpho-functional properties in response to pathology or innate changes of these cells can lead to pathologies. Overall pathological changes in astroglia are complex and diverse and often vary with different disease stages. We classify astrogliopathologies into reactive astrogliosis, astrodegeneration with astroglial atrophy and loss of function, and pathological remodelling of astrocytes. Such changes can occur in neurological, neurodevelopmental, metabolic and psychiatric disorders as well as in infection and toxic insults. Mutation in astrocyte-specific genes leads to specific pathologies, such as Alexander disease, which is a leukodystrophy. We discuss changes in astroglia in the pathological context and identify some molecular entities underlying pathology. These entities within astroglia may repent targets for novel therapeutic intervention in the management of brain pathologies.

Aceruloplasminemia: Waiting for an Efficient Therapy

Aceruloplasminemia is an ultra-rare hereditary disorder caused by defective production of ceruloplasmin. Its phenotype is characterized by iron-restricted erythropoiesis and tissue iron overload, diabetes, and progressive retinal and neurological degeneration. Ceruloplasmin is a ferroxidase that plays a critical role in iron homeostasis through the oxidation and mobilization of iron from stores and subsequent incorporation of ferric iron into transferrin (Tf), which becomes available for cellular uptake via the Tf receptor. In addition, ceruloplasmin has antioxidant properties preventing the production of deleterious reactive oxygen species via the Fenton reaction. Some recent findings suggest that aceruloplasminemia phenotypes can be more heterogeneous than previously believed, varying within a wide range. Within this large heterogeneity, microcytosis with or without anemia, low serum iron and high serum ferritin, and diabetes are the early hallmarks of the disease, while neurological manifestations appear 10-20 years later. The usual therapeutic approach is based on iron chelators that are efficacious in reducing systemic iron overload. However, they have demonstrated poor efficacy in counteracting the progression of neurologic manifestations, and also often aggravate anemia, thereby requiring drug discontinuation. Open questions remain regarding the mechanisms leading to neurological manifestation and development of diabetes, and iron chelation therapy (ICT) efficacy. Recent studies in animal models of aceruloplasminemia support the possibility of new therapeutic approaches by parenteral ceruloplasmin administration. In this review we describe the state of the art of aceruloplasminemia with particular attention on the pathogenic mechanisms of the disease and therapeutic approaches, both current and perspective.

Nexus between mitochondrial function, iron, copper and glutathione in Parkinson's disease

Parkinson's disease is neuropathologically characterised by loss of catecholamine neurons in vulnerable brain regions including substantia nigra pars compacta and locus coeruleus. This review discusses how the susceptibility of these regions is defined by their shared biochemical characteristics that differentiate them from other neurons. Parkinson's disease is biochemically characterised by mitochondrial dysfunction, accumulation of iron, diminished copper content and depleted glutathione levels in these regions. This review also discusses this neuropathology, and provides evidence for how these pathological features are mechanistically linked to each other. This leads to the conclusion that disruption of mitochondrial function, or iron, copper or glutathione metabolism in isolation provokes the pathological impairment of them all. This creates a vicious cycle that drives pathology leading to mitochondrial failure and neuronal cell death in vulnerable brain regions.

Neurodegeneration with brain iron accumulation

Neurodegeneration with brain iron accumulation (NBIA) describes a heterogeneous group of inherited rare clinical and genetic entities. Clinical core symptoms comprise a combination of early-onset dystonia, pyramidal and extrapyramidal signs with ataxia, cognitive decline, behavioral abnormalities, and retinal and axonal neuropathy variably accompanying these core features. Increased nonphysiologic, nonaging-associated brain iron, most pronounced in the basal ganglia, is often termed the unifying characteristic of these clinically variable disorders, though occurrence and extent can be fluctuating or even absent. Neuropathologically, NBIA disorders usually are associated with widespread axonal spheroids and local iron accumulation in the basal ganglia. Postmortem, Lewy body, TDP-43, or tau pathology has been observed. Genetics have fostered ongoing progress in elucidating underlying pathophysiologic mechanisms of NBIA disorders. Ten associated genes have been established, with many more being suggested as new technologies and data emerge. Clinically, certain symptom combinations can suggest a specific genetic defect. Genetic tests, combined with postmortem neuropathology, usually make for the final disease confirmation. Despite these advances, treatment to date remains mainly symptomatic. This chapter reviews the established genetic defects leading to different NBIA subtypes, highlights phenotypic presentations to direct genetic testing, and briefly discusses the scarce available treatment options and upcoming challenges and future hopes of the field.

Coexistence of Copper in the Iron-Rich Particles of Aceruloplasminemia Brain

The interaction between iron and copper has been discussed in association with human health and diseases for many years. Ceruloplasmin, a multi-copper oxidase, is mainly involved in iron metabolism and its genetic defect, aceruloplasminemia (ACP), shows neurological disorders and diabetes associated with excessive iron accumulation, but little is known about the state of copper in the brain. Here, we investigated localization of these metals in the brains of three patients with ACP using electron microscopes equipped with an energy-dispersive x-ray analyzer. Histochemically, iron deposition was observed mainly in the basal ganglia and dentate nucleus, and to lesser degree in the cerebral cortex of the patients, whereas copper grains were not detected. X-ray microanalysis identified two types of iron-rich particles in their brains: dense bodies, namely hemosiderins, and their aggregated inclusions. A small number of hemosiderins and most inclusions contained a significant amount of copper which was enough for distinct Cu x-ray images. These copper-containing particles were observed more frequently in the putamen and dentate nucleus than the cerebral cortex. Coexistence of iron and copper was supported by good correlations in the molecular ratios between these two metals in iron-rich particles with Cu x-ray image. Iron-dependent copper accumulation in iron-rich particles may suggest that copper recycling is enhanced to meet the increased requirement of cuproproteins in iron overload brain. In conclusion, the iron-rich particles with Cu x-ray image were found in the ACP brain.

Review: Insights into molecular mechanisms of disease in neurodegeneration with brain iron accumulation: unifying theories

Neurodegeneration with brain iron accumulation (NBIA) is a group of disorders characterized by dystonia, parkinsonism and spasticity. Iron accumulates in the basal ganglia and may be accompanied by Lewy bodies, axonal swellings and hyperphosphorylated tau depending on NBIA subtype. Mutations in 10 genes have been associated with NBIA that include Ceruloplasmin (Cp) and ferritin light chain (FTL), both directly involved in iron homeostasis, as well as Pantothenate Kinase 2 (PANK2), Phospholipase A2 group 6 (PLA2G6), Fatty acid hydroxylase 2 (FA2H), Coenzyme A synthase (COASY), C19orf12, WDR45 and DCAF17 (C2orf37). These genes are involved in seemingly unrelated cellular pathways, such as lipid metabolism, Coenzyme A synthesis and autophagy. A greater understanding of the cellular pathways that link these genes and the disease mechanisms leading to iron dyshomeostasis is needed. Additionally, the major overlap seen between NBIA and more common neurodegenerative diseases may highlight conserved disease processes. In this review, we will discuss clinical and pathological findings for each NBIA-related gene, discuss proposed disease mechanisms such as mitochondrial health, oxidative damage, autophagy/mitophagy and iron homeostasis, and speculate the potential overlap between NBIA subtypes.

Astrocyte Dysfunction in Developmental Neurometabolic Diseases

Astrocytes play crucial roles in maintaining brain homeostasis and in orchestrating neural development, all through tightly coordinated steps that cooperate to maintain the balance needed for normal development. Here, we review the alterations in astrocyte functions that contribute to a variety of developmental neurometabolic disorders and provide additional data on the predominant role of astrocyte dysfunction in the neurometabolic neurodegenerative disease glutaric acidemia type I. Finally, we describe some of the therapeutical approaches directed to neurometabolic diseases and discuss if astrocytes can be possible therapeutic targets for treating these disorders.

The role of hepcidin in chronic mild stress-induced depression

Depression is one of the most prevalent challenges of mental conditions. Yet its exact etiology has not been clear. Chronic stress increases the production of cytokines, which can lead to depression. Hepcidin, an iron modulator, is involved in the inflammation process as well as iron homeostasis. This study was designed to investigate the role of hepcidin, on stress-induced depression. 60 male wistar rats were entered the experiment. We used a chronic unpredictable mild stress (for 28 days) as a rat model of depression. In stressed group, three subgroups were treated with three different doses of dalteparin (a hepcidin inhibitor): 70IU/kg, 100IU/kg and 140IU/kg daily, for 4 weeks. The animals in the stressed group had more depressive-like behavior than the control group. Moreover, chronic mild stress produced an increased serum interleukin-6 levels. These effects were accompanied by an obvious increase in hepcidin mRNA level and iron content in the hippocampus. These changes were blocked by the injection of dalteparin. In conclusion, inhibition of hepcidin may reduce many pathological changes seen in stress-induced depressive disorders.

Iron transport across the blood-brain barrier: development, neurovascular regulation and cerebral amyloid angiopathy

There are two barriers for iron entry into the brain: (1) the brain-cerebrospinal fluid (CSF) barrier and (2) the blood-brain barrier (BBB). Here, we review the literature on developmental iron accumulation by the brain, focusing on the transport of iron through the brain microvascular endothelial cells (BMVEC) of the BBB. We review the iron trafficking proteins which may be involved in the iron flux across BMVEC and discuss the plausible mechanisms of BMVEC iron uptake and efflux. We suggest a model for how BMVEC iron uptake and efflux are regulated and a mechanism by which the majority of iron is trafficked across the developing BBB under the direct guidance of neighboring astrocytes. Thus, we place brain iron uptake in the context of the neurovascular unit of the adult brain. Last, we propose that BMVEC iron is involved in the aggregation of amyloid-β peptides leading to the progression of cerebral amyloid angiopathy which often occurs prior to dementia and the onset of Alzheimer's disease.

Metal and complementary molecular bioimaging in Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia in the elderly, affecting over 27 million people worldwide. AD represents a complex neurological disorder which is best understood as the consequence of a number of interconnected genetic and lifestyle variables, which culminate in multiple changes to brain structure and function. These can be observed on a gross anatomical level in brain atrophy, microscopically in extracellular amyloid plaque and neurofibrillary tangle formation, and at a functional level as alterations of metabolic activity. At a molecular level, metal dyshomeostasis is frequently observed in AD due to anomalous binding of metals such as Iron (Fe), Copper (Cu), and Zinc (Zn), or impaired regulation of redox-active metals which can induce the formation of cytotoxic reactive oxygen species and neuronal damage. Metal chelators have been administered therapeutically in transgenic mice models for AD and in clinical human AD studies, with positive outcomes. As a result, neuroimaging of metals in a variety of intact brain cells and tissues is emerging as an important tool for increasing our understanding of the role of metal dysregulation in AD. Several imaging techniques have been used to study the cerebral metallo-architecture in biological specimens to obtain spatially resolved data on chemical elements present in a sample. Hyperspectral techniques, such as particle-induced X-ray emission (PIXE), energy dispersive X-ray spectroscopy (EDS), X-ray fluorescence microscopy (XFM), synchrotron X-ray fluorescence (SXRF), secondary ion mass spectrometry (SIMS), and laser ablation inductively coupled mass spectrometry (LA-ICPMS) can reveal relative intensities and even semi-quantitative concentrations of a large set of elements with differing spatial resolution and detection sensitivities. Other mass spectrometric and spectroscopy imaging techniques such as laser ablation electrospray ionization mass spectrometry (LA ESI-MS), MALDI imaging mass spectrometry (MALDI-IMS), and Fourier transform infrared spectroscopy (FTIR) can be used to correlate changes in elemental distribution with the underlying pathology in AD brain specimens. Taken together, these techniques provide new techniques to probe the pathobiology of AD and pave the way for identifying new therapeutic targets. The current review aims to discuss the advantages and challenges of using these emerging elemental and molecular imaging techniques, and highlight clinical achievements in AD research using bioimaging techniques.

Neuroglia in ageing and disease

The proper operation of the mammalian brain requires dynamic interactions between neurones and glial cells. Various types of glial cells are susceptible to morpho-functional changes in a variety of brain pathological states, including toxicity, neurodevelopmental, neurodegenerative and psychiatric disorders. Morphological modifications include a change in the glial cell size and shape; the latter is evident by changes of the appearance and number of peripheral processes. The most blatant morphological change is associated with the alteration of the sheer number of neuroglia cells in the brain. Functionally, glial cells can undergo various metabolic and biochemical changes, the majority of which reflect upon homeostasis of neurotransmitters, in particular that of glutamate, as well as on defence mechanisms provided by neuroglia. Not only glial cells exhibit changes associated with the pathology of the brain but they also change with brain aging.

Astroglia in neurological diseases

Astroglia encompass a subset of versatile glial cells that fulfill a major homeostatic role in the mammalian brain. Since any brain disease results from failure in brain homeostasis, astroglial cells are involved in many, if not all, aspects of neurological and/or psychiatric disorders. In this article, the roles of astrocytes as homeostatic cells in healthy and diseased brains are surveyed. These cells can mount the defence response to the insult of the brain, astrogliosis, when and where they display hypertrophy. Interestingly, astrocytes can alternatively display atrophy in some pathological conditions. Various pathologies, including Alexander and Alzheimer's diseases, amyotrophic lateral sclerosis, stroke and epilepsy, to mention a few, are discussed. Astrocytes could represent a novel target for medical intervention in the treatment of brain disorders.

The neuropathology of neurodegeneration with brain iron accumulation

Neuropathology plays a key role in characterizing the pathogenesis of neurodegenerative diseases including forms of neurodegeneration with brain iron accumulation (NBIA). Despite important differences, several genetically diverse forms of NBIA nevertheless share common features in addition to iron deposition, such as the presence of neuroaxonal spheroids. Multiple forms of NBIA also demonstrate tau or synuclein pathology, suggesting parallels with both Alzheimer and Parkinson diseases. This chapter summarizes what has been learned from the study of human patient tissues. Gross and microscopic findings are delineated, and similarities and differences between forms of NBIA are presented. Neuropathologic findings often help characterize fundamental features of disease and provide a springboard for more focused hypothesis-driven studies. Lessons learned from neuropathology thus contribute much to the characterization of the molecular mechanisms of disease.

Aceruloplasminemia: an update

Aceruloplasminemia is an inherited neurodegenerative disorder involving "neurodegeneration with brain iron accumulation," which is caused by genetic defects in the ceruloplasmin gene. Ceruloplasmin is a multicopper oxidase with ferroxidase activity that oxidizes ferrous iron following its transfer to extracellular transferrin. In the central nervous system, a glycosylphosphatidylinositol-linked ceruloplasmin bound to the cell membranes was found to be the major isoform of this protein. Aceruloplasminemia is characterized by diabetes, retinal degeneration, and progressive neurological symptoms, including extrapyramidal symptoms, ataxia, and dementia. Clinical and pathological studies and investigations of cell culture and murine models revealed that there is an iron-mediated cellular radical injury caused by a marked accumulation of iron in the affected parenchymal tissues. The aim of this chapter is to provide an overview of not only the clinical features, genetic and molecular pathogenesis, and treatment of aceruloplasminemia but also the biological and physiological features of iron metabolism.

Genetics and Pathophysiology of Neurodegeneration with Brain Iron Accumulation (NBIA)

Our understanding of the syndromes of Neurodegeneration with Brain Iron Accumulation (NBIA) continues to grow considerably. In addition to the core syndromes of pantothenate kinase-associated neurodegeneration (PKAN, NBIA1) and PLA2G6-associated neurodegeneration (PLAN, NBIA2), several other genetic causes have been identified (including FA2H, C19orf12, ATP13A2, CP and FTL). In parallel, the clinical and pathological spectrum has broadened and new age-dependent presentations are being described. There is also growing recognition of overlap between the different NBIA disorders and other diseases including spastic paraplegias, leukodystrophies and neuronal ceroid lipofuscinosis which makes a diagnosis solely based on clinical findings challenging. Autopsy examination of genetically-confirmed cases demonstrates Lewy bodies, neurofibrillary tangles, and other hallmarks of apparently distinct neurodegenerative disorders such as Parkinson's disease (PD) and Alzheimer's disease. Until we disentangle the various NBIA genes and their related pathways and move towards pathogenesis-targeted therapies, the treatment remains symptomatic. Our aim here is to provide an overview of historical developments of research into iron metabolism and its relevance in neurodegenerative disorders. We then focus on clinical features and investigational findings in NBIA and summarize therapeutic results reviewing reports of iron chelation therapy and deep brain stimulation. We also discuss genetic and molecular underpinnings of the NBIA syndromes.

Excess iron harms the brain: the syndromes of neurodegeneration with brain iron accumulation (NBIA)

Regulation of iron metabolism is crucial: both iron deficiency and iron overload can cause disease. In recent years, our understanding of the syndromes of Neurodegeneration with Brain Iron Accumulation (NBIA) continues to grow considerably. These are characterized by excessive iron deposition in the brain, mainly the basal ganglia. Pantothenate kinase-associated neurodegeneration (PKAN, NBIA1) and PLA2G6-associated neurodegeneration (PLAN, NBIA2) are the core syndromes, but several other genetic causes have been identified (including FA2H, C19orf12, ATP13A2, CP and FTL). These conditions show a wide clinical and pathological spectrum, with clinical overlap between the different NBIA disorders and other diseases including spastic paraplegias, leukodystrophies, and neuronal ceroid lipofuscinosis. Lewy body pathology was confirmed in some clinical subtypes (C19orf12-associated neurodegeneration and PLAN). Research aims at disentangling the various NBIA genes and their related pathways to move towards pathogenesis-targeted therapies. Until then treatment remains symptomatic. Here we will introduce the group of NBIA syndromes and review the main clinical features and investigational findings.

The National NeuroAIDS Tissue Consortium brain gene array: two types of HIV-associated neurocognitive impairment

Background

The National NeuroAIDS Tissue Consortium (NNTC) performed a brain gene expression array to elucidate pathophysiologies of Human Immunodeficiency Virus type 1 (HIV-1)-associated neurocognitive disorders.

Methods

Twenty-four human subjects in four groups were examined A) Uninfected controls; B) HIV-1 infected subjects with no substantial neurocognitive impairment (NCI); C) Infected with substantial NCI without HIV encephalitis (HIVE); D) Infected with substantial NCI and HIVE. RNA from neocortex, white matter, and neostriatum was processed with the Affymetrix® array platform.

Results

With HIVE the HIV-1 RNA load in brain tissue was three log₁₀ units higher than other groups and over 1,900 gene probes were regulated. Interferon response genes (IFRGs), antigen presentation, complement components and CD163 antigen were strongly upregulated. In frontal neocortex downregulated neuronal pathways strongly dominated in HIVE, including GABA receptors, glutamate signaling, synaptic potentiation, axon guidance, clathrin-mediated endocytosis and 14-3-3 protein. Expression was completely different in neuropsychologically impaired subjects without HIVE. They had low brain HIV-1 loads, weak brain immune responses, lacked neuronally expressed changes in neocortex and exhibited upregulation of endothelial cell type transcripts. HIV-1-infected subjects with normal neuropsychological test results had upregulation of neuronal transcripts involved in synaptic transmission of neostriatal circuits.

Interpretation

Two patterns of brain gene expression suggest that more than one pathophysiological process occurs in HIV-1-associated neurocognitive impairment. Expression in HIVE suggests that lowering brain HIV-1 replication might improve NCI, whereas NCI without HIVE may not respond in kind; array results suggest that modulation of transvascular signaling is a potentially promising approach. Striking brain regional differences highlighted the likely importance of circuit level disturbances in HIV/AIDS. In subjects without impairment regulation of genes that drive neostriatal synaptic plasticity reflects adaptation. The array provides an infusion of public resources including brain samples, clinicopathological data and correlative gene expression data for further exploration (http://www.nntc.org/gene-array-project).

Impairment of interrelated iron- and copper homeostatic mechanisms in brain contributes to the pathogenesis of neurodegenerative disorders

Iron and copper are important co-factors for a number of enzymes in the brain, including enzymes involved in neurotransmitter synthesis and myelin formation. Both shortage and an excess of iron or copper will affect the brain. The transport of iron and copper into the brain from the circulation is strictly regulated, and concordantly protective barriers, i.e., the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier (BCB) have evolved to separate the brain environment from the circulation. The uptake mechanisms of the two metals interact. Both iron deficiency and overload lead to altered copper homeostasis in the brain. Similarly, changes in dietary copper affect the brain iron homeostasis. Moreover, the uptake routes of iron and copper overlap each other which affect the interplay between the concentrations of the two metals in the brain. The divalent metal transporter-1 (DMT1) is involved in the uptake of both iron and copper. Furthermore, copper is an essential co-factor in numerous proteins that are vital for iron homeostasis and affects the binding of iron-response proteins to iron-response elements in the mRNA of the transferrin receptor, DMT1, and ferroportin, all highly involved in iron transport. Iron and copper are mainly taken up at the BBB, but the BCB also plays a vital role in the homeostasis of the two metals, in terms of sequestering, uptake, and efflux of iron and copper from the brain. Inside the brain, iron and copper are taken up by neurons and glia cells that express various transporters.

Extensive brain pathology in a patient with aceruloplasminemia with a prolonged duration of illness

We report the sixth autopsy case of a patient with aceruloplasminemia. He was the younger brother of the first reported autopsy case of this disease. Among autopsy cases with aceruloplasminemia reported to date, he had the longest duration of neurologic disorders. The neuropathologic findings showed that the basal ganglia and dentate nuclei were most severely affected. The most striking finding in the present case was that marked iron deposition was evident in the cerebral cortex. Many enlarged or deformed astrocytes and globular structures, both of which were heavily iron loaded, were found in the cerebral cortex as well as in the basal ganglia. Pyramidal neurons in his cerebral cortex were fewer in number than observed in the previous reported cases. There was a negative correlation between the number of cortical pyramidal neurons and globular structures. The present case clearly indicates that the neuropathologic process in aceruloplasminemia extends beyond the basal ganglia to the cerebral cortex with time.

Ceruloplasmin protects against rotenone-induced oxidative stress and neurotoxicity

To clarify the neuroprotective property of ceruloplasmin and the pathogenesis of aceruloplasminemia, we generated ceruloplasmin-deficient (CP⁻/⁻) mice on the C57BL/10 genetic background and further treated them with a mitochondrial complex I inhibitor, rotenone. There was no iron accumulation in the brains of CP⁻/⁻ mice at least up to 60 weeks of age. Without rotenone treatment, CP⁻/⁻ mice showed slight motor dysfunction compared with CP⁺/⁺ mice, but there were no detectable differences in the levels of oxidative stress markers between these two groups. A low dose of rotenone did not affect the mitochondrial complex I activity in our mice, however, it caused a significant change in motor behavior, neuropathology, or the levels of oxidative stress markers in CP⁻/⁻ mice, but not in CP⁺/⁺ mice. Our data support that ceruloplasmin protects against rotenone-induced oxidative stress and neurotoxicity, probably through its antioxidant properties independently of its function of iron metabolism.

Astrocytes: biology and pathology

Astrocytes are specialized glial cells that outnumber neurons by over fivefold. They contiguously tile the entire central nervous system (CNS) and exert many essential complex functions in the healthy CNS. Astrocytes respond to all forms of CNS insults through a process referred to as reactive astrogliosis, which has become a pathological hallmark of CNS structural lesions. Substantial progress has been made recently in determining functions and mechanisms of reactive astrogliosis and in identifying roles of astrocytes in CNS disorders and pathologies. A vast molecular arsenal at the disposal of reactive astrocytes is being defined. Transgenic mouse models are dissecting specific aspects of reactive astrocytosis and glial scar formation in vivo. Astrocyte involvement in specific clinicopathological entities is being defined. It is now clear that reactive astrogliosis is not a simple all-or-none phenomenon but is a finely gradated continuum of changes that occur in context-dependent manners regulated by specific signaling events. These changes range from reversible alterations in gene expression and cell hypertrophy with preservation of cellular domains and tissue structure, to long-lasting scar formation with rearrangement of tissue structure. Increasing evidence points towards the potential of reactive astrogliosis to play either primary or contributing roles in CNS disorders via loss of normal astrocyte functions or gain of abnormal effects. This article reviews (1) astrocyte functions in healthy CNS, (2) mechanisms and functions of reactive astrogliosis and glial scar formation, and (3) ways in which reactive astrocytes may cause or contribute to specific CNS disorders and lesions.

The role of astroglia in neuroprotection

Astrocytes are the main neural cell type responsible for the maintenance of brain homeostasis. They form highly organized anatomical domains that are interconnected into extensive networks. These features, along with the expression of a wide array of receptors, transporters, and ion channels, ideally position them to sense and dynamically modulate neuronal activity. Astrocytes cooperate with neurons on several levels, including neurotransmitter trafficking and recycling, ion homeostasis, energy metabolism, and defense against oxidative stress. The critical dependence of neurons upon their constant support confers astrocytes with intrinsic neuroprotective properties which are discussed here. Conversely, pathogenic stimuli may disturb astrocytic function, thus compromising neuronal functionality and viability. Using neuroinflammation, Alzheimer's disease, and hepatic encephalopathy as examples, we discuss how astrocytic defense mechanisms may be overwhelmed in pathological conditions, contributing to disease progression.

Iron localization in superficial siderosis of the central nervous system

Originally conceived as an uncommon disorder, with the advent of MRI, CNS superficial siderosis has been observed more frequently. We present histologic, histochemical, immunohistochemical, immunofluorescent and ultrastructural evaluation of a 56-year-old woman with superficial siderosis. Iron was concentrated in macrophages, superficial astrocytes and gray matter oligodendroglia deep within the cord. While spatially associated with dystrophic glial and neuronal spheroids, iron did not colocalize with mitochondria. Neurotoxic effects were observed despite selective iron localization only within a variety of non-neuronal cell types.

Ceruloplasmin alters the tissue disposition and neurotoxicity of manganese, but not its loading onto transferrin

Manganese (Mn) is a redox-active element, and whereas its uptake, disposition, and toxicity in mammals may depend in part on its oxidation state, the proteins affecting manganese oxidation state and speciation in vivo are not well known. Studies have suggested that the oxidase protein ceruloplasmin (Cp) mediates iron and manganese oxidation and loading onto plasma transferrin (Tf), as well as cellular iron efflux. We hypothesized that ceruloplasmin may also affect the tissue distribution and eventual neurotoxicity of manganese. To test this, aceruloplasminemic versus wild-type mice were treated with a single i.p. (54)Mn tracer dose, or elevated levels of manganese subchronically (0, 7.5, or 15 mg Mn/kg s.c., three doses per week for 4 weeks), and evaluated for transferrin-bound manganese, blood manganese partitioning, tissue manganese disposition, and levels of brain glutathione, thiobarbituric acid reactive substances (TBARS), and protein carbonyls as measures of oxidative stress, and open arena activity. Results show that ceruloplasmin does not play a role in the loading of manganese onto plasma transferrin in vivo, or in the partitioning of manganese between the plasma and cellular fractions of whole blood. Ceruloplasmin did, however, affect the retention of manganese in blood and its distribution to tissues, most notably kidney and to a lesser extent brain and lung. Results also indicate that ceruloplasmin interacted with chronic elevated manganese exposures to produce greater levels of brain oxidative stress. These results provide evidence that metal oxidase proteins play an important role in altering neurotoxicity arising from elevated manganese exposures.

Copper and iron disorders of the brain

Copper and iron are transition elements essential for life. These metals are required to maintain the brain's biochemistry such that deficiency or excess of either copper or iron results in central nervous system disease. This review focuses on the inherited disorders in humans that directly affect copper or iron homeostasis in the brain. Elucidation of the molecular genetic basis of these rare disorders has provided insight into the mechanisms of copper and iron acquisition, trafficking, storage, and excretion in the brain. This knowledge permits a greater understanding of copper and iron roles in neurobiology and neurologic disease and may allow for the development of therapeutic approaches where aberrant metal homeostasis is implicated in disease pathogenesis.

Brain iron metabolism: neurobiology and neurochemistry

New findings obtained during the past years, especially the discovery of mutations in the genes associated with brain iron metabolism, have provided key insights into the homeostatic mechanisms of brain iron metabolism and the pathological mechanisms responsible for neurodegenerative diseases. The accumulated evidence demonstrates that misregulation in brain iron metabolism is one of the initial causes for neuronal death in some neurodegenerative disorders. The errors in brain iron metabolism found in these disorders have a multifactorial pathogenesis, including genetic and nongenetic factors. The disturbances of iron metabolism might occur at multiple levels, including iron uptake and release, storage, intracellular metabolism and regulation. It is the increased brain iron that triggers a cascade of deleterious events, leading to neuronal death in these diseases. In the article, the recent advances in studies on neurochemistry and neuropathophysiology of brain iron metabolism were reviewed.

A proteomic approach to studying the differentiation of neural stem cells

The mechanisms that regulate the maintenance of stem cell self-renewal versus differentiation are complex and remain mostly unknown. Understanding neurogenesis and neural cell differentiation presents a unique challenge for the treatment of nervous system disorders. To gain more insight into molecular mechanisms of the differentiation of neural cells, we combined the advantage of porcine fetal neural stem cells (NSCs) in vitro differentiation model and proteomic analysis. Using 2-DE followed by MS, we profiled constituent proteins of NSCs and their differentiated progenies at first and then indicated protein species that were significantly up- or down-regulated during the differentiation. The largest identified group of constituent proteins was related to RNA and protein metabolism and processing, including chaperones, and the second largest consisted of proteins involved in cell organization (cytoskeleton and annexins). Differentiation of neural cells was found to be accompanied by changes in the expression of proteins involved in DNA and RNA binding, mRNA processing and transport, stress responses, iron storage, and redox regulation. Additional immunoblot analysis verified the induction of alpha-B crystallin and heterogeneous nuclear ribonucleoproteins (hnRNPs) A1 and A2/B1. Furthermore, immunocytochemistry demonstrated specific localization of alpha-B crystallin in the cytoplasm or nucleus of glial cells and confirmed cellular expression patterns of hnRNPs A1 and A2/B1. These findings represent a significant step towards understanding neural cell differentiation and identification of the regulatory proteins associated with this process.

The pivotal role of astrocytes in the metabolism of iron in the brain

Iron is essential for the normal functioning of cells but since it is also capable of generating toxic reactive oxygen species, the metabolism of iron is tightly regulated. The present article advances the view that astrocytes are largely responsible for distributing iron in the brain. Capillary endothelial cells are separated from the neuropil by the endfeet of astrocytes, so astrocytes are ideally positioned to regulate the transport of iron to other brain cells and to protect them if iron breaches the blood-brain barrier. Astrocytes do not appear to have a high metabolic requirement for iron yet they possess transporters for transferrin, haemin and non-transferrin-bound iron. They store iron efficiently in ferritin and can export iron by a mechanism that involves ferroportin and ceruloplasmin. Since astrocytes are a common site of abnormal iron accumulation in ageing and neurodegenerative disorders, they may represent a new therapeutic target for the treatment of iron-mediated oxidative stress.

Ceruloplasmin and what it might do

The blue coloured plasma protein ceruloplasmin binds up to 95% of circulating copper, and has several possible functions. It has been proposed to function in copper transport, oxidation of organic amines, iron(II) oxidation and the regulation of cellular iron levels, and catechols, radical scavenging and other antioxidant processes. This account will consider the relative importance of these multiple functions in terms of the physiological roles of ceruloplasmin.

Brain Iron Toxicity: Differential Responses of Astrocytes, Neurons, and Endothelial Cells

Iron accumulation or iron overload in brain is commonly associated with neurodegenerative disorders such as Parkinson's and Alzheimer's diseases, and also plays a role in cellular damage following hemorrhagic stroke and traumatic brain injury. Despite the brain's highly regulated system for iron utilization and metabolism, these disorders often present following disruptions within iron metabolic pathways. Such dysregulation allows saturation of proteins involved in iron transport and storage, and may cause an increase in free ferrous iron within brain leading to oxidative damage. Not only do astrocytes, neurons, and brain endothelial cells serve unique purposes within the brain, but their individual cell types are equipped with distinct protective mechanisms against iron-induced injury. This review evaluates iron metabolism within the brain under homeostatic and pathological conditions and focuses on the mechanism(s) of brain cellular iron toxicity and differential responses of astrocytes, neurons, and brain vascular endothelial cells to excessive free iron.

Aluminum stimulates uptake of non-transferrin bound iron and transferrin bound iron in human glial cells

Aluminum and other trivalent metals were shown to stimulate uptake of transferrin bound iron and nontransferrin bound iron in erytholeukemia and hepatoma cells. Because of the association between aluminum and Alzheimer's Disease, and findings of higher levels of iron in Alzheimer's disease brains, the effects of aluminum on iron homeostasis were examined in a human glial cell line. Aluminum stimulated dose- and time-dependent uptake of nontransferrin bound iron and iron bound to transferrin. A transporter was likely involved in the uptake of nontransferrin iron because uptake reached saturation, was temperature-dependent, and attenuated by inhibitors of protein synthesis. Interestingly, the effects of aluminum were not blocked by inhibitors of RNA synthesis. Aluminum also decreased the amount of iron bound to ferritin though it did not affect levels of divalent metal transporter 1. These results suggest that aluminum disrupts iron homeostasis in the brain by several mechanisms including the transferrin receptor, a nontransferrin iron transporter, and ferritin.

Brain iron metabolism

Brain iron uptake is regulated by the expression of transferrin receptor 1 in endothelial cells of the blood-brain barrier. Transferrin-bound iron in the systemic circulation is endocytosed by brain endothelial cells, and elemental iron is released to brain interstitial fluid, likely by the iron exporter, ferroportin. Transferrin synthesized by oligodendrocytes in the brain binds much of the iron that traverses the blood-brain barrier after oxidation of the iron, most likely by a glycophosphosinositide-linked ceruloplasmin found in astrocytic foot processes that ensheathe brain endothelial cells. Neurons acquire iron from diferric transferrin, but it is less clear how glial cells acquire iron. In aging mammals, iron accumulates in the basal ganglia, and iron accumulation is believed to contribute to neurodegenerative diseases, including Parkinson and Alzheimer disease. Here we consider the possibility that iron accumulations, which are often thought to facilitate free radical generation and oxidative damage, may contain insoluble iron that is unavailable for cellular use, and the pathology associated with iron accumulations may result from functional iron deficiency in some diseases.