Juvenile-onset generalized neuroaxonal dystrophy (Hallervorden-Spatz disease) with diffuse neurofibrillary and lewy body pathology

Mitochondrial Toxicant-Induced Neuronal Apoptosis in Parkinson's Disease: What We Know so Far

Parkinson's disease (PD) is one of the most common progressive neurodegenerative diseases caused by the loss of dopamine-producing neuronal cells in the region of substantia nigra pars compacta of the brain. During biological aging, neuronal cells slowly undergo degeneration, but the rate of cell death increases tremendously under some pathological conditions, leading to irreversible neurodegenerative diseases. By the time symptoms of PD usually appear, more than 50 to 60% of neuronal cells have already been destroyed. PD symptoms often start with tremors, followed by slow movement, stiffness, and postural imbalance. The etiology of PD is still unknown; however, besides genetics, several factors contribute to neurodegenerative disease, including exposure to pesticides, environmental chemicals, solvents, and heavy metals. Postmortem brain tissues of patients with PD show mitochondrial abnormalities, including dysfunction of the electron transport chain. Most chemicals present in our environment have been shown to target the mitochondria; remarkably, patients with PD show a mild deficiency in NADH dehydrogenase activity, signifying a possible link between PD and mitochondrial dysfunction. Inhibition of electron transport complexes generates free radicals that further attack the macromolecules leading to neuropathological conditions. Apart from that, oxidative stress also causes neuroinflammation-mediated neurodegeneration due to the activation of microglial cells. However, the mechanism that causes mitochondrial dysfunction, especially the electron transport chain, in the pathogenesis of PD remains unclear. This review discusses the recent updates and explains the possible mechanisms of mitochondrial toxicant-induced neuroinflammation and neurodegeneration in PD.

An Insight into the Molecular Mechanism of Mitochondrial Toxicant-induced Neuronal Apoptosis in Parkinson's Disease

Parkinson's disease (PD) is one of the most common progressive neurodegenerative disorders affecting approximately 1% of the world's population at the age of 50 and above. Majority of PD cases are sporadic and show symptoms after the age of 60 and above. At that time, most of the dopaminergic neurons in the region of substantia nigra pars compacta have been degenerated. Although in past decades, discoveries of genetic mutations linked to PD have significantly impacted our current understanding of the pathogenesis of this devastating disorder, it is likely that the environment also plays a critical role in the etiology of sporadic PD. Recent epidemiological and experimental studies indicate that exposure to environmental agents, including a number of agricultural and industrial chemicals, may contribute to the pathogenesis of several neurodegenerative disorders, including PD. Furthermore, there is a strong correlation between mitochondrial dysfunction and several forms of neurodegenerative disorders, including Alzheimer's disease (AD), Huntington's disease (HD), Amyotrophic lateral sclerosis (ALS) and PD. Interestingly, substantia nigra of patients with PD has been shown to have a mild deficiency in mitochondrial respiratory electron transport chain NADH dehydrogenase (Complex I) activity. This review discusses the role of mitochondrial toxicants in the selective degeneration of dopaminergic neurons targeting the electron transport system that leads to Parkinsonism.

Tau and TDP-43 proteinopathies: kindred pathologic cascades and genetic pleiotropy

We review the literature on Tau and TDP-43 proteinopathies in aged human brains and the relevant underlying pathogenetic cascades. Complex interacting pathways are implicated in Alzheimer's disease and related dementias (ADRD), wherein multiple proteins tend to misfold in a manner that is "reactive," but, subsequently, each proteinopathy may contribute strongly to the clinical symptoms. Tau proteinopathy exists in brains of individuals across a broad spectrum of primary underlying conditions-e.g., developmental, traumatic, and inflammatory/infectious diseases. TDP-43 proteinopathy is also expressed in a wide range of clinical disorders.  Although TDP-43 proteinopathy was first described in the central nervous system of patients with amyotrophic lateral sclerosis (ALS) and in subtypes of frontotemporal dementia (FTD/FTLD), TDP-43 proteinopathy is also present in chronic traumatic encephalopathy, cognitively impaired persons in advanced age with hippocampal sclerosis, Huntington's disease, and other diseases. We list known Tau and TDP-43 proteinopathies.  There is also evidence of cellular co-localization between Tau and TDP-43 misfolded proteins, suggesting common pathways or protein interactions facilitating misfolding in one protein by the other. Multiple pleiotropic gene variants can alter risk for Tau or TDP-43 pathologies, and certain gene variants (e.g., APOE ε4, Huntingtin triplet repeats) are associated with increases of both Tau and TDP-43 proteinopathies. Studies of genetic risk factors have provided insights into multiple nodes of the pathologic cascades involved in Tau and TDP-43 proteinopathies. Variants from a specific gene can be either a low-penetrant risk factor for a group of diseases, or alternatively, a different variant of the same gene may be a disease-driving allele that is associated with a relatively aggressive and early-onset version of a clinically and pathologically specific disease type. Overall, a complex but enlightening paradigm has emerged, wherein both Tau and TDP-43 proteinopathies are linked to numerous overlapping upstream influences, and both are associated with multiple downstream pathologically- and clinically-defined deleterious effects.

New Perspectives in Iron Chelation Therapy for the Treatment of Neurodegenerative Diseases

Iron chelation has been introduced as a new therapeutic concept for the treatment of neurodegenerative diseases with features of iron overload. At difference with iron chelators used in systemic diseases, effective chelators for the treatment of neurodegenerative diseases must cross the blood–brain barrier. Given the promissory but still inconclusive results obtained in clinical trials of iron chelation therapy, it is reasonable to postulate that new compounds with properties that extend beyond chelation should significantly improve these results. Desirable properties of a new generation of chelators include mitochondrial destination, the center of iron-reactive oxygen species interaction, and the ability to quench free radicals produced by the Fenton reaction. In addition, these chelators should have moderate iron binding affinity, sufficient to chelate excessive increments of the labile iron pool, estimated in the micromolar range, but not high enough to disrupt physiological iron homeostasis. Moreover, candidate chelators should have selectivity for the targeted neuronal type, to lessen unwanted secondary effects during long-term treatment. Here, on the basis of a number of clinical trials, we discuss critically the current situation of iron chelation therapy for the treatment of neurodegenerative diseases with an iron accumulation component. The list includes Parkinson’s disease, Friedreich’s ataxia, pantothenate kinase-associated neurodegeneration, Huntington disease and Alzheimer’s disease. We also review the upsurge of new multifunctional iron chelators that in the future may replace the conventional types as therapeutic agents for the treatment of neurodegenerative diseases.

Exploring Missense Mutations in Tyrosine Kinases Implicated with Neurodegeneration

Protein kinases are one of the largest families of evolutionarily related proteins and the third most common protein class of human genome. All the protein kinases share the same structural organization. They are made up of an extracellular domain, transmembrane domain and an intra cellular kinase domain. Missense mutations in these kinases have been studied extensively and correlated with various neurological disorders. Individual mutations in the kinase domain affect the functions of protein. The enhanced or reduced expression of protein leads to hyperactivation or inactivation of the signalling pathways, resulting in neurodegeneration. Here, we present extensive analyses of missense mutations in the tyrosine kinase focussing on the neurodegenerative diseases encompassing structure function relationship. This is envisaged to enhance our understanding about the neurodegeneration and possible therapeutic measures.

Novel antibodies to phosphorylated α-synuclein serine 129 and NFL serine 473 demonstrate the close molecular homology of these epitopes

Pathological inclusions containing aggregated, highly phosphorylated (at serine129) α-synuclein (αS pSer129) are characteristic of a group of neurodegenerative diseases termed synucleinopathies. Antibodies to the pSer129 epitope can be highly sensitive in detecting αS inclusions in human tissue and experimental models of synucleinopathies. However, the generation of extensively specific pSer129 antibodies has been problematic, in some cases leading to the misinterpretation of αS inclusion pathology. One common issue is cross-reactivity to the low molecular mass neurofilament subunit (NFL) phosphorylated at Ser473. Here, we generated a series of monoclonal antibodies to the pSer129 αS and pSer473 NFL epitopes. We determined the relative abilities of the known αS kinases, polo-like kinases (PLK) 1, 2 and 3 and casein kinase (CK) II in phosphorylating NFL and αS, while using this information to characterize the specificity of the new antibodies. NFL can be phosphorylated by PLK1, 2 and 3 at Ser473; however CKII shows the highest phosphorylation efficiency and specificity for this site. Conversely, PLK3 is the most efficient kinase at phosphorylating αS at Ser129, but there is overlay in the ability of these kinases to phosphorylate both epitopes. Antibody 4F8, generated to the pSer473 NFL epitope, was relatively specific for phosphorylated NFL, however it could uniquely cross-react with pSer129 αS when highly phosphorylated, further showing the structural similarity between these phospho-epitopes. All of the new pSer129 antibodies detected pathological αS inclusions in human brains and mouse and cultured cell experimental models of induced synucleinopathies. Several of these pSer129 αS antibodies reacted with the pSer473 NFL epitope, but 2 clones (LS3-2C2 and LS4-2G12) did not. However, LS3-2C2 demonstrated cross-reactivity with other proteins. Our findings further demonstrate the difficulties in generating specific pSer129 αS antibodies, but highlights that the use of multiple antibodies, such as those generated here, can provide a sensitive and accurate assessment of αS pathology.

Parkinson's disease as a member of Prion-like disorders

Parkinson's disease is one of several neurodegenerative diseases associated with a misfolded, aggregated and pathological protein. In Parkinson's disease this protein is alpha-synuclein and its neuronal deposits in the form of Lewy bodies are considered a hallmark of the disease. In this review we describe the clinical and experimental data that have led to think of alpha-synuclein as a prion-like protein and we summarize data from in vitro, cellular and animal models supporting this view.

Neurodegeneration with brain iron accumulation: update on pathogenic mechanisms

Perturbation of iron distribution is observed in many neurodegenerative disorders, including Alzheimer’s and Parkinson’s disease, but the comprehension of the metal role in the development and progression of such disorders is still very limited. The combination of more powerful brain imaging techniques and faster genomic DNA sequencing procedures has allowed the description of a set of genetic disorders characterized by a constant and often early accumulation of iron in specific brain regions and the identification of the associated genes; these disorders are now collectively included in the category of neurodegeneration with brain iron accumulation (NBIA). So far 10 different genetic forms have been described but this number is likely to increase in short time. Two forms are linked to mutations in genes directly involved in iron metabolism: neuroferritinopathy, associated to mutations in the FTL gene and aceruloplasminemia, where the ceruloplasmin gene product is defective. In the other forms the connection with iron metabolism is not evident at all and the genetic data let infer the involvement of other pathways: Pank2, Pla2G6, C19orf12, COASY, and FA2H genes seem to be related to lipid metabolism and to mitochondria functioning, WDR45 and ATP13A2 genes are implicated in lysosomal and autophagosome activity, while the C2orf37 gene encodes a nucleolar protein of unknown function. There is much hope in the scientific community that the study of the NBIA forms may provide important insight as to the link between brain iron metabolism and neurodegenerative mechanisms and eventually pave the way for new therapeutic avenues also for the more common neurodegenerative disorders. In this work, we will review the most recent findings in the molecular mechanisms underlining the most common forms of NBIA and analyze their possible link with brain iron metabolism.

Phenotypes and genotypes of patients with pantothenate kinase-associated neurodegeneration in Asian and Caucasian populations: 2 cases and literature review

Objectives. Pantothenate kinase-associated neurodegeneration (PKAN) is a rare disease caused by pantothenate kinase 2 (PANK2, OMIM 606157) mutations. This study is aimed to investigate clinical presentations, pathologies, and genetics in patients with PKAN. Methods. Two patients with PKAN were reported. We reviewed the literature to include additional 19 patients with PKAN in Eastern Asia. These patients were divided into classic and atypical groups by the age of onset. We compared the data on PKAN patients of Asian and Caucasian populations. Results. We found iron deposits in the globus pallidus in our Patient 1 and a heterozygous truncating mutation (c.1408insT) in Patient 2. Literature review shows that generalized dystonia and bulbar signs are more common in classic PKAN patients, whereas segmental dystonia and tremors are more specific to atypical ones. Asian patients have less complex presentations—lower prevalence of pyramidal signs, mental impairment, and parkinsonism—than Caucasians. D378G in exon 3 is the most frequent mutation (28%) in Asians. Conclusions. Our study demonstrates that the distribution of dystonia is the major distinction between subgroups of PKAN. Caucasian patients have more complex presentations than Asians. Exon 3 and 4 are hot spots for screening PANK2 mutations in Asian patients.

The function of α-synuclein

Human genetics has indicated a causal role for the protein α-synuclein in the pathogenesis of familial Parkinson's disease (PD), and the aggregation of synuclein in essentially all patients with PD suggests a central role for this protein in the sporadic disorder. Indeed, the accumulation of misfolded α-synuclein now defines multiple forms of neural degeneration. Like many of the proteins that accumulate in other neurodegenerative disorders, however, the normal function of synuclein remains poorly understood. In this article, we review the role of synuclein at the nerve terminal and in membrane remodeling. We also consider the prion-like propagation of misfolded synuclein as a mechanism for the spread of degeneration through the neuraxis.

Extensive aggregation of α-synuclein and tau in juvenile-onset neuroaxonal dystrophy: an autopsied individual with a novel mutation in the PLA2G6 gene-splicing site

BACKGROUND

Infantile neuroaxonal dystrophy (INAD) is a rare autosomal-recessive neurodegenerative disorder. Patients with INAD usually show neurological symptoms with infant onset and die in childhood. Recently, it was reported that mutations in the PLA2G6 gene cause INAD, but neuropathological analysis of genetically confirmed individuals with neuroaxonal dystrophy has been limited.

RESULTS

Here, we report a Japanese individual with neuroaxonal dystrophy associated with compound heterozygous mutations in the PLA2G6 gene. A novel splice-site mutation resulting in skipping and missense mutations (p.R538C) in exon 9 was identified in the patient. This patient initially presented with cerebellar ataxia at the age of 3 years, which was followed by symptoms of mental retardation, extrapyramidal signs, and epileptic seizure. The patient survived until 20 years of age. Neuropathological findings were characterized by numerous axonal spheroids, brain iron deposition, cerebellar neuronal loss, phosphorylated alpha-synuclein-positive Lewy bodies (LBs), and phosphorylated-tau-positive neurofibrillary tangles. In particular, LB pathology exhibited a unique distribution with extremely severe cortical involvement.

CONCLUSIONS

Our results support a genetic clinical view that compound heterozygous mutations with potential residual protein function are associated with a relatively mild phenotype. Moreover, the severe LB pathology suggests that dysfunction of the PLA2G6 gene primarily contributes to LB formation.

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.

Syndromes of neurodegeneration with brain iron accumulation

In parallel to recent developments of genetic techniques, understanding of the syndromes of neurodegeneration with brain iron accumulation has grown considerably. The acknowledged clinical spectrum continues to broaden, with age-dependent presentations being recognized. Postmortem brain examination of genetically confirmed cases has demonstrated Lewy bodies and/or tangles in some forms, bridging the gap to more common neurodegenerative disorders, including Parkinson disease. In this review, the major forms of neurodegeneration with brain iron accumulation (NBIA) are summarized, concentrating on clinical findings and molecular insights. In addition to pantothenate kinase-associated neurodegeneration (PKAN) and phospholipase A2-associated neurodegeneration (PLAN), fatty acid hydroxylase-associated neurodegeneration (FAHN) NBIA, mitochondrial protein-associated neurodegeneration, Kufor-Rakeb disease, aceruloplasminemia, neuroferritinopathy, and SENDA syndrome (static encephalopathy of childhood with neurodegeneration in adulthood) are discussed.

Neuroimaging features of neurodegeneration with brain iron accumulation

NBIA characterizes a class of neurodegenerative diseases that feature a prominent extrapyramidal movement disorder, intellectual deterioration, and a characteristic deposition of iron in the basal ganglia. The diagnosis of NBIA is made on the basis of the combination of representative clinical features along with MR imaging evidence of iron accumulation. In many cases, confirmatory molecular genetic testing is now available as well. A number of new subtypes of NBIA have recently been described, with distinct neuroradiologic and clinical features. This article outlines the known subtypes of NBIA, delineates their clinical and radiographic features, and suggests an algorithm for evaluation.

Neuropathology underlying clinical variability in patients with synucleinopathies

Abnormal aggregates of the synaptic protein, α-synuclein, are the dominant pathology in syndromes known as the synucleinopathies. The cellular aggregation of the protein occurs in three distinct types of inclusions in three main clinical syndromes. α-Synuclein deposits in neuronal Lewy bodies and Lewy neurites in idiopathic Parkinson's disease (PD) and dementia with Lewy bodies (DLB), as well as incidentally in a number of other conditions. In contrast, α-synuclein deposits largely in oligodendroglial cytoplasmic inclusions in multiple system atrophy (MSA). Lastly, α-synuclein also deposits in large axonal spheroids in a number of rarer neuroaxonal dystrophies. Disorders are usually defined by their most dominant pathology, but for the synucleinopathies, clinical heterogeneity within the main syndromes is well documented. MSA was originally viewed as three different clinical phenotypes due to different anatomical localization of the lesions. In PD, recent meta-analyses have identified four main clinical phenotypes, and clinicopathological correlations suggest that more severe and more rapid progression of pathology with chronological age, as well as the involvement of additional neuropathologies, differentiates these phenotypes. In DLB, recent large studies show that clinical diagnosis is too insensitive to identify the syndrome itself, although clinicopathological studies suggest variable clinical features occur in the different pathological forms of this syndrome (pure DLB, DLB with Alzheimer's disease (AD), and AD with amygdala predominant Lewy pathology). The recognition of considerable heterogeneity within the synucleinopathy syndromes is important for the identification of factors involved in changing their pathological phenotype.

Novel histopathologic findings in molecularly-confirmed pantothenate kinase-associated neurodegeneration

Pantothenate kinase-associated neurodegeneration is a form of neurodegeneration with brain iron accumulation, characterized by a progressive movement disorder and prominent iron deposition in the globus pallidus. Formerly referred to as Hallervorden-Spatz syndrome, the disorder was renamed pantothenate kinase-associated neurodegeneration after discovery of the causative gene, PANK2. Although the pathological features of clinically characterized Hallervorden-Spatz syndrome have been described, the literature is confounded by the historical use of this term for nearly all conditions with prominent basal ganglia iron accumulation and by the fact that this term encompasses a genetically heterogeneous group of disorders, now referred to as 'neurodegeneration with brain iron accumulation'. As a result, interpreting reports that precede molecular characterization of specific forms of neurodegeneration with brain iron accumulation is problematic. In the present studies, we describe neuropathological findings in six cases of molecularly confirmed pantothenate kinase-associated neurodegeneration. We identify prominent ubiquinated deposits in pantothenate kinase-associated neurodegeneration. We also characterize two distinct origins of spheroid bodies and delineate histological features of iron deposition. In so doing, we characterize fundamental features of the disease and redefine its nosological relationship to other neurodegenerative disorders.

Defective FA2H leads to a novel form of neurodegeneration with brain iron accumulation (NBIA)

OBJECTIVE

Neurodegeneration with brain iron accumulation (NBIA) represents a distinctive phenotype of neurodegenerative disease for which several causative genes have been identified. The spectrum of neurologic disease associated with mutations in NBIA genes is broad, with phenotypes that range from infantile neurodegeneration and death in childhood to adult-onset parkinsonism-dystonia. Here we report the discovery of a novel gene that leads to a distinct form of NBIA.

METHODS

Using autozygosity mapping and candidate gene sequencing, we identified mutations in the fatty acid hydroxylase gene FA2H, newly implicating abnormalities of ceramide metabolism in the pathogenesis of NBIA.

RESULTS

Neuroimaging demonstrated T2 hypointensity in the globus pallidus, confluent T2 white matter hyperintensities, and profound pontocerebellar atrophy in affected members of two families. Phenotypically, affected family members exhibited spastic quadriparesis, ataxia, and dystonia with onset in childhood and episodic neurological decline. Analogous to what has been reported previously for PLA2G6, the phenotypic spectrum of FA2H mutations is diverse based on our findings and those of prior investigators, because FA2H mutations have been identified in both a form of hereditary spastic paraplegia (SPG35) and a progressive familial leukodystrophy.

INTERPRETATION

These findings link white matter degeneration and NBIA for the first time and implicate new signaling pathways in the genesis of NBIA.

The miR-15/107 group of microRNA genes: evolutionary biology, cellular functions, and roles in human diseases

The miR-15/107 group of microRNA (miRNA) gene is increasingly appreciated to serve key functions in humans. These miRNAs regulate gene expression involved in cell division, metabolism, stress response, and angiogenesis in vertebrate species. The miR-15/107 group has also been implicated in human cancers, cardiovascular disease and neurodegenerative disease, including Alzheimer's disease. Here we provide an overview of the following: (1) the evolution of miR-15/107 group member genes; (2) the expression levels of miRNAs in mammalian tissues; (3) evidence for overlapping gene-regulatory functions by different miRNAs; (4) the normal biochemical pathways regulated by miR-15/107 group miRNAs; and (5) the roles played by these miRNAs in human diseases. Membership in this group is defined based on sequence similarity near the mature miRNAs' 5' end: all include the sequence AGCAGC. Phylogeny of this group of miRNAs is incomplete; thus, a definitive taxonomic classification (e.g., designation as a "superfamily") is currently not possible. While all vertebrates studied to date express miR-15a, miR-15b, miR-16, miR-103, and miR-107, mammals alone are known to express miR-195, miR-424, miR-497, miR-503, and miR-646. Multiple different miRNAs in the miR-15/107 group are expressed at moderate to high levels in human tissues. We present data on the expression of all known miR-15/107 group members in human cerebral cortical gray matter and white matter using new miRNA profiling microarrays. There is extensive overlap in the mRNAs targeted by miR-15/107 group members. We show new data from cultured H4 cancer cells that demonstrate similarities in mRNAs targeted by miR-16 and miR-103 and also support the importance of the mature miRNAs' 5' seed region in mRNA target recognition. In conclusion, the miR-15/107 group of miRNA genes is a fascinating topic of study for evolutionary biologists, miRNA biochemists, and clinically oriented translational researchers alike.

Disrupted membrane homeostasis and accumulation of ubiquitinated proteins in a mouse model of infantile neuroaxonal dystrophy caused by PLA2G6 mutations

Mutations in the PLA2G6 gene, which encodes group VIA calcium-independent phospholipase A2 (iPLA(2)beta), were recently identified in patients with infantile neuroaxonal dystrophy (INAD) and neurodegeneration with brain iron accumulation. A pathological hallmark of these childhood neurodegenerative diseases is the presence of distinctive spheroids in distal axons that contain accumulated membranes. We used iPLA(2)beta-KO mice generated by homologous recombination to investigate neurodegenerative consequences of PLA2G6 mutations. iPLA(2)beta-KO mice developed age-dependent neurological impairment that was evident in rotarod, balance, and climbing tests by 13 months of age. The primary abnormality underlying this neurological impairment was the formation of spheroids containing tubulovesicular membranes remarkably similar to human INAD. Spheroids were strongly labeled with anti-ubiquitin antibodies. Accumulation of ubiquitinated protein in spheroids was evident in some brain regions as early as 4 months of age, and the onset of motor impairment correlated with a dramatic increase in ubiquitin-positive spheroids throughout the neuropil in nearly all brain regions. Furthermore accumulating ubiquitinated proteins were observed primarily in insoluble fractions of brain tissue, implicating protein aggregation in this pathogenic process. These results indicate that loss of iPLA(2)beta causes age-dependent impairment of axonal membrane homeostasis and protein degradation pathways, leading to age-dependent neurological impairment. iPLA(2)beta-KO mice will be useful for further studies of pathogenesis and experimental interventions in INAD and neurodegeneration with brain iron accumulation.

Tau-predominant-associated pathology in a sporadic late-onset Hallervorden-Spatz syndrome

Hallervorden-Spatz syndrome (HSS) is a heterogeneous clinicopathological disorder currently included within the broader title of neurodegeneration with brain iron accumulation (NBIA). The classic histological hallmarks of HSS are axonal spheroids and excessive iron-containing granules accompanied by neuronal loss and gliosis in the globus pallidus and substantia nigra reticulata. In the modern literature, attention has been drawn to the co-occurrence of two other histological markers: Lewy bodies mainly composed of abnormal alpha-synuclein, and neurofibrillary tangles due to hyperphosphorilated tau aggregation. Discrepancies exist regarding the importance of these molecular changes and its relevance for the nosology of HSS. Most authors have emphasized the importance of the Lewy body-like pathology, favoring the inclusion of HSS within the alpha-synucleinopathies. We report on a case of late-onset HSS, with the typical histological findings restricted to the basal ganglia and cerebellum in which tau pathology was exceedingly more abundant than alpha-synuclein pathology. This case contributes to the increasing evidence about the heterogeneity of HSS. We favor the view that the molecular changes and the protein misfolding underlying the Lewy body and tangle formation in HSS/NBIA are secondary to the main pathological process and should not be taken as the basis for its nosological classification.

The distribution pattern of pathology and cholinergic deficits in amygdaloid complex in Alzheimer's disease and dementia with Lewy bodies

We studied the distribution pattern of pathology and cholinergic deficits in the subnuclei of the amygdaloid complex (AC) in five patients with Alzheimer's disease (AD), eight with dementia with Lewy bodies (DLB) and five normal controls. In controls, the basal nucleus contained the highest choline acetyltransferase activity; the activity in the lateral and central nuclei and those in the cortical, medial and accessory basal nuclei were comparable. In AD, there was a significant decrease in choline acetyltransferase activity in the accessory basal and lateral nuclei, in DLB a significant decrease was observed in the accessory basal, lateral and cortical nuclei. Compared to controls the hyperphosphorylated tau-pathology burden was significantly higher in the basal, central and medial nuclei in AD and in the central, cortical, lateral and medial nuclei in DLB. The amyloid plaque burden was significantly higher in the accessory basal, basal, lateral and cortical nuclei in AD and in all nuclei in DLB. The alpha-synuclein burden was significantly higher in all nuclei in both AD and DLB. Compared to AD alpha-synuclein burden was higher in all nuclei in DLB. There were no correlations between the distribution pattern of hyperphosphorylated tau-pathology, amyloid plaques and alpha-synuclein-positive structures, and choline acetyltransferase activity, except the lateral nucleus in DLB. In conclusion we found no relationship between the pattern of cholinergic deficits and the distribution pattern of lesions in the AC of patients with AD or DLB. Cholinergic deficits were more prominent in the nuclei of basolateral (BL) group in AD, whereas the nuclei of both BL and corticomedial groups were involved in DLB, which may be due to the involvement of both basal forebrain and brainstem cholinergic nuclei in the latter.

Altered neuronal mitochondrial coenzyme A synthesis in neurodegeneration with brain iron accumulation caused by abnormal processing, stability, and catalytic activity of mutant pantothenate kinase 2

Mutations in the pantothenate kinase 2 (PANK2) gene have been identified in patients with neurodegeneration with brain iron accumulation (NBIA; formerly Hallervorden-Spatz disease). However, the mechanisms by which these mutations cause neurodegeneration are unclear, especially given the existence of multiple pantothenate kinase genes in humans and multiple PanK2 transcripts with potentially different subcellular localizations. We demonstrate that PanK2 protein is localized to mitochondria of neurons in human brain, distinguishing it from other pantothenate kinases that do not possess mitochondrial-targeting sequences. PanK2 protein translated from the most 5' start site is sequentially cleaved at two sites by the mitochondrial processing peptidase, generating a long-lived 48 kDa mature protein identical to that found in human brain extracts. The mature protein catalyzes the initial step in coenzyme A (CoA) synthesis but displays feedback inhibition in response to species of acyl CoA rather than CoA itself. Some, but not all disease-associated point mutations result in significantly reduced catalytic activity. The most common mutation, G521R, results in marked instability of the intermediate PanK2 isoform and reduced production of the mature isoform. These results suggest that NBIA is caused by altered neuronal mitochondrial lipid metabolism caused by mutations disrupting PanK2 protein levels and catalytic activity.

Sporadic fatal insomnia with spongiform degeneration in the thalamus and widespread PrPSc deposits in the brain

We report a case of human prion disease of 29 months duration in a 74-year-old Japanese man. The disease started with progressive sleeplessness and dementia. MRI showed gradually progressive cerebral atrophy. Neuronal loss, spongiform change and gliosis were evident in the thalamus and cerebral cortex, as well as in the striatum and amygdaloid nucleus. In the cerebellar cortex, mild-to-moderate depletion of Pukinje cells and spongiform change were observed. Mild neuronal loss in the inferior olivary nucleus was also seen. Immunohistochemistry revealed widespread perivacuolar deposits of abnormal prion protein (PrPsc) in the cerebral cortex, thalamus, basal ganglia, and brainstem, and minimal plaque-like deposits of PrPSc in the cerebellar cortex. In the cerebellar plaque-like deposits, the presence of amyloid fibrils was confirmed ultrastructurally. The entire pathology appeared to lie halfway between those of CJD and fatal insomnia, and further demonstrated the relationship between spongiform degeneration and PrPSc deposits, especially in the diseased thalamus. By immunoblotting, the thalamus was shown to contain the lowest amount of PrPSc among the brain regions examined. The PrPSc of type 2, in which the ratio of the three glycoforms was compatible with that of sporadic fatal insomnia (MM2-thalamic variant) reported previously, was also demonstrated. Analysis of the prion protein gene (PRNP) showed no mutation, and homozygosity for methionine at codon 129. In conclusion, we considered that this patient had been suffering from sporadic, pathologically atypical fatal insomnia.

Mutations in the pantothenate kinase gene PANK2 are not associated with Parkinson disease

Pantothenate kinase-associated neurodegeneration (PKAN) may serve as a model for Parkinson disease (PD) since many PKAN patients suffer from parkinsonism and both conditions lead to iron accumulation in the basal ganglia. We screened the gene coding for pantothenate kinase 2 (PANK2) for sequence variants in PD. We found no mutations in 67 PD patients with affected sibs or early-onset disease. Moreover, PANK2 polymorphisms were not associated with late-onset idiopathic PD in 339 patients. We conclude that PANK2 variants exert, if any, only a very small effect in the genetic risk of PD.

Tau and α-Synuclein Inclusions in a Case of Familial Frontotemporal Dementia and Progressive Aphasia

Recent studies have shown that neurofibrillary tangles are frequently accompanied by alpha-synuclein inclusions in sporadic and familial Alzheimer disease, in Down syndrome, in progressive supranuclear palsy, and Parkinsonism dementia complex of Guam. Here we report the cases of 2 brothers with familial progressive aphasia who developed features of frontotemporal dementia with predominant tau pathology but also alpha-synuclein pathology. The 2 patients' brains revealed abundant tau pathology in the hippocampus and basal ganglia, whereas tau and alpha-synuclein aggregates coexisted only in the nucleus basalis of Meynert, the only region where alpha-synuclein was present. In this brain region, abundant Lewy bodies, Lewy neurites, and tau inclusions were found; the pathology was more abundant in the older than in the younger brother. Sarkosyl-insoluble tau extracted from brains of the 2 patients showed the presence of tau filaments that contained 3 major tau bands of 60, 64, and 68 kDa on Western blot analysis. These bands contained mainly tau with 3 and 4 repeats and no amino-terminal inserts and tau with 4 repeats and one amino-terminal insert. No mutations were identified in the tau, alpha-synuclein, beta-synuclein, or parkin genes. We think that this is the first report showing a specific colocalization of neurofibrillary tangles and Lewy bodies in a family with progressive aphasia.

Speech rate as a sticky switch: a multiple lesion case analysis of mutism and hyperlalia

Though it has long been known on the basis of clinical associations and serendipitous observation that speech rate is related to mood and psychomotor baseline, it is less known that speech rate is also related to libido and to immune function. We make the case for a bipolar phenomenon of "psychic tonus," encompassing all these dimensions. The elated, agitated, libidinal, immunofacilitated, and talkative pole is an "approach" disposition primarily activated by the normal left hemisphere-especially, though not exclusively, its frontal lobe. The dejected, lethargic, delibidinized, immunosuppressed, and mute pole is an "avoidance" disposition primarily activated by the normal right hemisphere-especially, though not exclusively, its frontal lobe. In support of this proposed model, we present new evidence, via meta-analysis of previously published single lesion case reports, of a highly significant association between right hemisphere lesions and non-aphasic hyperlalia, and between left hemisphere lesions and non-aphasic mutism.

Neuropathological spectrum of synucleinopathies

Synucleinopathies comprise a diverse group of neurodegenerative proteinopathies that share common pathological lesions composed of aggregates of conformational and posttranslational modifications of alpha-synuclein in selected populations of neurons and glia. Abnormal filamentous aggregates of misfolded alpha-synuclein protein are the major components of Lewy bodies, dystrophic (Lewy) neurites, and the Papp-Lantos filaments in oligodendroglia and neurons in multiple system atrophy linked to degeneration of affected brain regions. The synucleinopathies include (1) Lewy body disorders and dementia with Lewy bodies, (2) multiple system atrophy (MSA), and (3) Hallervorden-Spatz disease. (1) The pathological diagnosis of Lewy body disorders and dementia with Lewy bodies is established by validated consensus criteria based on semiquantitative assessment of subcortical and cortical Lewy bodies as their common hallmarks. They are accompanied by subcortical multisystem degeneration with neuronal loss and gliosis with or without Alzheimer pathologic state. Lewy bodies also occur in numerous other disorders, including pure autonomic failure, neuroaxonal dystrophies, and various amyloidoses and tauopathies. (2) Multiple system atrophy, a sporadic, adult-onset degenerative movement disorder of unknown cause, is characterized by alpha-synuclein-positive glial cytoplasmic and rare neuronal inclusions throughout the central nervous system associated with striatonigral degeneration, olivopontocerebellar atrophy, and involvement of medullar and spinal autonomic nuclei. (3) In neurodegeneration with brain iron accumulation type I, or Hallervorden-Spatz disease, alpha-synuclein is present in axonal spheroids and glial and neuronal inclusions. While the identity of the major components of Lewy bodies suggests that a pathway leading from normal soluble to abnormal misfolded filamentous proteins is central for their pathogenesis, regardless of the primary disorder, there are conformational differences in alpha-synuclein between neuronal and glial aggregates, showing nonuniform mapping for its epitopes. Despite several cellular and transgenic models, it is not clear whether inclusion body formation is an adaptive/neuroprotective or a pathogenic reaction/process generated in response to different, mostly undetermined, functional triggers linked to neurodegeneration.

Familial Lewy body diseases

Lewy body disease includes clinically and pathologically defined disorders in which Lewy bodies occur in the nervous system. In recent years, the molecular features of these disorders have been emerging. Several genetic loci have been identified in association with familial Lewy body disease; however, the genetic risks underlying most cases of familial Lewy body disease remain to be discovered. The fact that Lewy bodies stain strongly with antibodies to asynuclein and that mutations in the alpha-synuclein gene lead to syndromes in which parkinsonism and dementia occur gives us important clues regarding the biologic processes leading to disease. Pursuit of additional mendelian causes of familial Lewy body disease and study of the factors contributing to the complex phenotypes associated with Lewy body disorders will elucidate underlying disease pathways and, thus, possible targets for therapeutic intervention.

Phosphorylated alpha-synuclein is ubiquitinated in alpha-synucleinopathy lesions

alpha-Synuclein is one of the major components of intracellular fibrillary aggregates in the brains of a subset of neurodegenerative disorders, including Parkinson's disease, dementia with Lewy bodies, multiple system atrophy, and Hallervorden-Spatz disease, which are referred to as alpha-synucleinopathies. We have shown previously (Fujiwara, H., Hasegawa, M., Dohmae, N., Kawashima, A., Masliah, E., Goldberg, M. S., Shen, J., Takio, K., and Iwatsubo, T. (2002) Nat. Cell Biol. 4, 160-164) that alpha-synuclein deposited in synucleinopathy brains is extensively phosphorylated at Ser-129 and migrates at 15 kDa. Here we examined the biochemical characteristics of the additional, higher molecular mass species of phosphorylated alpha-synuclein-positive polypeptides that also are recovered in the Sarkosyl-insoluble fraction of synucleinopathy and migrate at about 22 and 29 kDa. These 22 and 29 kDa bands were positive for three different anti-ubiquitin antibodies and comigrated perfectly with in vitro ubiquitinated alpha-synuclein that may correspond to mono- and diubiquitinated alpha-synuclein, respectively. Furthermore, cyanogen bromide cleavage of the 22 and 29 kDa polypeptides shifted the mobility to 19 and 26 kDa, respectively, and they retained immunoreactivity for both ubiquitin and alpha-synuclein. Finally, protein sequence analysis showed that the 19 kDa band contained two amino-terminal sequences of alpha-synuclein and ubiquitin. These results strongly suggest that phosphorylated alpha-synuclein is targeted to mono- and diubiquitination in synucleinopathy brains, which may have implications for mechanisms of these diseases.

Upregulation of alpha-synuclein by lipopolysaccharide and interleukin-1 in human macrophages

Alpha-synuclein was originally identified as the presynaptic nerve terminal protein. Recently, we reported that alpha-synuclein is also expressed in cultured human astrocytes and that its levels are increased by stimulation with interleukin-1beta, suggesting that it may be involved in inflammatory processes. We therefore investigated the effect of inflammatory stimuli on alpha-synuclein expression in human macrophages. Alpha-synuclein mRNA and protein were detected in cultured human macrophages and levels of alpha-synuclein protein were increased by stimulation with lipopolysaccharide and interleukin-1beta in a time- and concentration-dependent manner. Immunofluorescent staining showed that alpha-synuclein protein was expressed within the cytoplasm and nucleus. Furthermore, alpha-synuclein immunoreactivity was present in alveolar macrophages from human lung tissues. These findings suggest that the function of alpha-synuclein is not exclusive to the nervous system and that alpha-synuclein may play a role in inflammatory processes and immune responses.

Genetics of parkinsonism

Parkinson's disease (PD) was noted to have a familial component as early as 1880 (Leroux, 1880). More recently, the discovery of several genetic factors influencing parkinsonism has emphasized the importance of heredity in PD. The clinical spectrum of familial parkinsonism is wide; it includes not only PD, but also dementia with Lewy bodies (DLB), progressive supranuclear palsy (PSP), essential tremor, and other disorders. In the general population, it is likely that PD results from combined genetic and environmental factors, most of which are not yet known. The discovery of causal mutations in the gene for alpha-synuclein, parkin, and of genetic linkages to chromosomes 2p4, 4p5, and three loci on 1q6-8 have revolutionized PD research. This review focuses on recent progress in the Mendelian genetics of PD and those diseases in which parkinsonism is a prominent feature, and considers how these discoveries modify our beliefs regarding the etiology and pathogenesis of these disorders.

Tau and alpha-synuclein pathology in amygdala of Parkinsonism-dementia complex patients of Guam

Amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) is a progressive neurodegenerative disorder of Chamorro residents of Guam and the Mariana Islands, characterized by abundant neuron loss and tau neurofibrillary pathology similar to that observed in Alzheimer's disease (AD). A variety of neurodegenerative diseases with tau pathology including ALS/PDC also have alpha-synuclein positive pathology, primarily in the amygdala. We further characterized the tau and alpha-synuclein pathology in the amygdala of a large series of 30 Chamorros using immunohistochemical and biochemical techniques. Tau pathology was readily detected in both affected and unaffected Chamorros. In contrast, alpha-synuclein pathology was detected in 37% of patients with PDC but not detected in Chamorros without PDC or AD. The alpha-synuclein aggregates often co-localized within neurons harboring neurofibrillary tangles suggesting a possible interaction between the two proteins. Tau and alpha-synuclein pathology within the amygdala is biochemically similar to that observed in AD and synucleinopathies, respectively. Thus, the amygdala may be selectively vulnerable to developing both tau and alpha-synuclein pathology or tau pathology may predispose it to synuclein aggregation. Furthermore, in PDC, tau and alpha-synuclein pathology occurs independent of beta-amyloid deposition in amygdala thereby implicating the aggregation of these molecules in the severe neurodegeneration frequently observed in this location.

Selective insolubility of alpha-synuclein in human Lewy body diseases is recapitulated in a transgenic mouse model

alpha-Synuclein (alpha-SYN) is deposited in intraneuronal cytoplasmic inclusions (Lewy bodies, LBs) characteristic for Parkinson's disease (PD) and LB dementias. alpha-SYN forms LB-like fibrils in vitro, in contrast to its homologue beta-SYN. Here we have investigated the solubility of SYNs in human LB diseases and in transgenic mice expressing human wild-type and PD-associated mutant [A30P]alpha-SYN driven by the brain neuron-specific promoter, Thy1. Distinct alpha-SYN species were detected in the detergent-insoluble fractions from brains of patients with PD, dementia with LBs, and neurodegeneration with brain iron accumulation type 1 (formerly known as Hallervorden-Spatz disease). Using the same extraction method, detergent-insolubility of human alpha-SYN was observed in brains of transgenic mice. In contrast, neither endogenous mouse alpha-SYN nor beta-SYN were detected in detergent-insoluble fractions from transgenic mouse brains. The nonamyloidogenic beta-SYN was incapable of forming insoluble fibrils because amino acids 73 to 83 in the central region of alpha-SYN are absent in beta-SYN. In conclusion, the specific accumulation of detergent-insoluble alpha-SYN in transgenic mice recapitulates a pivotal feature of human LB diseases.

The cellular pathology of Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder of unknown cause that occurs in adults. The presence of Lewy bodies (LB) in association with nerve cell loss in the substantia nigra and various other regions of the nervous system is a diagnostic hallmark of the disease. In 1997, a mutation was identified in the alpha-synuclein gene in families with autosomal dominant PD. Subsequent immunohistochemical studies have revealed that all of the LB in familial and sporadic PD contain the gene product alpha-synuclein: abnormal filaments that constitute LB were clearly recognized by antibodies against alpha-synuclein. Moreover, it was shown that the glial cells, both astrocytes and oligodendrocytes, are also affected by alpha-synuclein pathology. Recently, a novel protein, synphilin-1, has been identified that interacts with alpha-synuclein. Interestingly, synphilin-1 immunohistochemistry has demonstrated that this protein is present in the central core of classical (brainstem) LB, which are composed mainly of densely packed vesicular structures. The role of both alpha-synuclein and synphilin-1 in normal conditions has yet to be clarified.

Iron overload, oxidative stress, and axonal dystrophy in brain disorders

Hallervorden-Spatz syndrome is an autosomal-recessive brain disorder with signs of extrapyramidal dysfunction and mental deterioration, which associate with iron accumulation in globus pallidus and substantia nigra pars reticulata. Studies of oxidant stress in parkinsonian animal models suggest a linkage of iron overload to axonal dystrophy. Redox cycling of iron complexes (i.e., ferrous citrate and hemoglobin) increases hydroxyl radicals, lipid peroxidation, axonal dystrophy, and necrotic or apoptotic cell death. An increase of oxidative stress in the basal ganglia because of redox cycling of iron complexes leads to dopamine overflow and psychomotor dysfunction. Iron overload-induced axonal dystrophy has been demonstrated consistently using in vitro and in vivo models with a prominent feature of lipid peroxidation. This iron-induced oxidative stress is often accentuated by ascorbate and oxidized glutathione, although it is suppressed by the following antioxidants: S-nitrosoglutathione or nitric oxide, MnSOD mimics, manganese, U-78517F, Trolox, and deferoxamine. Preconditioning induction of stress proteins (i.e., hemeoxygenase-1 and neuronal nitric oxide synthase) and hypothermia therapy suppress the generation of toxic reactive oxygen, lipid, and thiol species evoked by bioactive iron complexes in the brain. Finally, combined antioxidative therapeutics and gene induction procedures may prove to be useful for slowing progressive neurodegeneration caused by iron overload in the brain.

Neurodegeneration with brain iron accumulation, type 1 is characterized by alpha-, beta-, and gamma-synuclein neuropathology

Neurodegeneration with brain iron accumulation, type 1 (NBIA 1), or Hallervorden-Spatz syndrome, is a rare neurodegenerative disorder characterized clinically by Parkinsonism, cognitive impairment, pseudobulbar features, as well as cerebellar ataxia, and neuropathologically by neuronal loss, gliosis, and iron deposition in the globus pallidus, red nucleus, and substantia nigra. The hallmark pathological lesions of NBIA 1 are axonal spheroids, but Lewy body (LB)-like intraneuronal inclusions, glial inclusions, and rare neurofibrillary tangles also occur. Here we show that there is an accumulation of alpha-synuclein (alphaS) in LB-like inclusions, glial inclusions, and spheroids in the brains of three NBIA 1 patients. Further, beta-synuclein (betaS) and gamma-synuclein (gammaS) immunoreactivity was detected in spheroids but not in LB-like or glial inclusions. Western blot analysis demonstrated high-molecular weight alphaS aggregates in the high-salt-soluble and Triton X-100-insoluble/sodium dodecyl sulfate-soluble fraction of the NBIA 1 brain. Significantly, the levels of alphaS were markedly reduced in the Triton X-100-soluble fractions compared to control brain, and unlike other synucleinopathies, insoluble alphaS did not accumulate in the formic acid-soluble fraction. These findings expand the concept of neurodegenerative synucleinopathies by implicating alphaS, betaS, and gammaS in the pathogenesis of NBIA 1.

Alpha-synuclein inclusions in amygdala in the brains of patients with the parkinsonism-dementia complex of Guam

We investigated by immunohistochemistry the deposition of alpha-synuclein in the brains of deceased patients with the parkinsonism-dementia complex (PDC) of Guam. Five of 13 PDC brains showed numerous alpha-synuclein positive neuronal inclusions and abnormal neurites, chiefly in the amygdala. Similar alpha-synuclein positive lesions were observed, although to a lesser extent, in the entorhinal cortex and the dorsal vagal nucleus. No alpha-synuclein positive inclusions were observed in motor cortex or locus coeruleus, and only a small number of positive inclusions were found in the Sommer's sector, temporal cortex, or substantia nigra. Some of the alpha-synuclein positive inclusions were reminiscent of cortical Lewy bodies (LB), but many of those in the amygdala coexisted with tau-positive pretangles and/or neurofibrillary tangles (NFT) within the same neurons. In these neurons, tau-positive shells encapsulated alpha-synuclein positive central cores or irregularly shaped alpha-synuclein-positive deposition intermingled with pretangles/NFT. Thus, the present study suggests that a common mechanism may govern aggregation of alpha-synuclein and tau in the amygdala, and that aggregation of alpha-synuclein may play some role in the neurodegenerative process of a tauopathy (i.e. PDC) in which Abeta deposition is virtually absent.