Neuronal intranuclear inclusions are ultrastructurally and immunologically distinct from cytoplasmic inclusions of neuronal intermediate filament inclusion disease

Renal ultrastructural damage induced by chronic exposure to copper oxide nanomaterials: Electron microscopy study

Copper oxide nanomaterials are used in many biomedical, agricultural, environmental, and industrial sectors with potential risk to human health and the environment. The present study was conducted to determine the renal ultrastructural damage caused by 25 nm CuO nanoparticles in renal tissues. Adult healthy male Wister Albino rats (Rattus norvegicus) were administered 35 intraperitoneal injections of CuO nanoparticles (2 mg/kg). Ultrastructural changes were evaluated using transmission electron microscopy techniques. The renal tissues of rats with subchronic exposure to CuO nanoparticles demonstrated glomerular alterations that included hypertrophic endothelial cells, dilated capillaries and occlusions, podocyte hypertrophy, pedicle disorganization, mesangial cell hyperplasia, and crystalloid precipitation. Moreover, the treated renal cells exhibited mitochondrial swelling and crystolysis, cytoplasmic vacoulization, lysosomal hypertrophy, apoptotic activity, endoplasmic reticulum dilatation, nuclear deformity, chromatin dissolution, and basement membrane thickening. In addition, disruption and disorganization of the renal cells microvilli together with cystolic inclusions were also detected. It was concluded from the present findings that CuO nanoparticles could interact with the components of the renal tissues in ways that could cause ultrastructural injury, suggesting renal tissue pathophysiology. Additional studies are suggested for a better understanding the nanotoxicity of CuO nanomaterials.

An autopsy case report of neuronal intermediate filament inclusion disease presenting with predominantly upper motor neuron features

We describe an autopsy case of neuronal intermediate filament inclusion disease (NIFID), a subtype of frontotemporal lobar degeneration (FTLD) with the appearance of fused-in-sarcoma (FUS) inclusions (FTLD-FUS). A 57-year-old man developed dysarthria and dysphagia. One year and five months later, he was admitted to a hospital, and pseudobulbar palsy and right upper motor neuron signs were observed on examination. Needle electromyography revealed no active or chronic denervation. His neurological symptoms gradually deteriorated, and behavioral alterations occurred. He died of hemoperitoneum secondary to rupture of a ureteric tumor. The total duration of the disease was six years and 10 months. Neuropathologically, the frontal cortex, including the motor cortex, and the pyramidal tract were severely affected, whereas the lower motor neurons in the spinal cord and brainstem were mildly damaged. The striatum and substantia nigra were also severely damaged. Hyaline conglomerate inclusions, neuronal cytoplasmic inclusions with a distinct eosinophilic core (so-called cherry spot), Pick body-like inclusions, and eosinophilic round inclusions were observed in the remaining neurons. Immunohistochemical examination revealed that these inclusions were immunoreactive for FUS. HC inclusions were also immunoreactive for α-internexin and phosphorylated neurofilament protein. FUS-immunoreactive NCIs were abundant in the basal ganglia but not in the hippocampus, in contrast to previously reported NIFID cases. Furthermore, Bunina bodies identified by immunohistochemistry for cystatin C were also observed in the lower motor neurons. Bunina bodies may be present in NIFID. This case confirms the pathological heterogeneity of NIFID and supports the notion of the difference between amyotrophic lateral sclerosis and NIFID.

Neuronal intranuclear inclusion disease: recognition and update

Neuronal intranuclear inclusion disease (NIID) used to be considered as a neurodegenerative disease. Due to the availability of skin biopsy, the diagnostic efficiency of the disease has been greatly improved. Recently, researchers have successfully identified that the GGC repeat expansion in the 5'-untranslated region of the NOTCH2NLC gene is the causative mutation of NIID. Besides the typical phenotype of brain degeneration, peripheral neuropathy, and autonomic disturbance, the gene mutation is also associated with Alzheimer's disease, frontotemporal dementia, Parkinson's disease, multiple system atrophy, essential tremor, adult leukoencephalopathy, and oculopharyngodistal myopathy. However, it still needs more studies to elucidate whether those variable NIID phenotypes can categorize into NOTCH2NLC repeat expansion related disorders. We update the discovery milestone, clinical phenotype, laboratory examinations, as well as new insight into the diagnosis and treatment of NIID. NIID is an unusual degenerative disease that can involve multiple systems, especially involves the nervous system. Originally, it is named after the pathological characteristics with extensive intranuclear eosinophilic inclusions in central and peripheral nervous tissues, as well as in multiple other organs (Sone et al., Brain 139:3170-3186, 2016). In 2019, several research teams from China and Japan have simultaneously identified that the GGC repeat expansion in the 5'-untranslated region (5'UTR) of the NOTCH2NLC gene is the pathogenic mutation of NIID (Ishiura et al., Nat Genet 51:1222-1232, 2019; Deng et al., J Med Genet 56:758-764, 2019; Sone et al., Nat Genet 51:1215-1221, 2019; Sun et al., Brain 143:222-233, 2020; Tian et al., Am J Hum Genet 105:166-176, 2019). Since then, the number of reported NIID cases is rapidly increasing, and the spectrum of NOTCH2NLC repeat expansion related disorders is significantly broadening (Westenberger and Klein, Brain 143:5-8, 2020). However, the NIID associated with GGC repeat expansion of the NOTCH2NLC gene might be account for a part of patients, probably more frequently in the Asian population, because this expansion has not been identified in an European series with postmortem confirmed NIID cases (Chen et al., Ann Clin Transl Neurol 2020). In order to better understand of the disease, we need to revisit the current state of NIID in combination with the findings based on our experiences in recent years and update the concepts about the clinical and pathogenic progression of NIID.

Specialized roles of neurofilament proteins in synapses: Relevance to neuropsychiatric disorders

Neurofilaments are uniquely complex among classes of intermediate filaments in being composed of four subunits (NFL, NFM, NFH and alpha-internexin in the CNS) that differ in structure, regulation, and function. Although neurofilaments have been traditionally viewed as axonal structural components, recent evidence has revealed that distinctive assemblies of neurofilament subunits are integral components of synapses, especially at postsynaptic sites. Within the synaptic compartment, the individual subunits differentially modulate neurotransmission and behavior through interactions with specific neurotransmitter receptors. These newly uncovered functions suggest that alterations of neurofilament proteins not only underlie axonopathy in various neurological disorders but also may play vital roles in cognition and neuropsychiatric diseases. Here, we review evidence that synaptic neurofilament proteins are a sizable population in the CNS and we advance the concept that changes in the levels or post-translational modification of individual NF subunits contribute to synaptic and behavioral dysfunction in certain neuropsychiatric conditions.

FUS immunogold labeling TEM analysis of the neuronal cytoplasmic inclusions of neuronal intermediate filament inclusion disease: a frontotemporal lobar degeneration with FUS proteinopathy

Fused in sarcoma (FUS)-immunoreactive neuronal and glial inclusions define a novel molecular pathology called FUS proteinopathy. FUS has been shown to be a component of inclusions of familial amyotrophic lateral sclerosis with FUS mutation and three frontotemporal lobar degeneration entities, including neuronal intermediate filament inclusion disease (NIFID). The pathogenic role of FUS is unknown. In addition to FUS, many neuronal cytoplasmic inclusions (NCI) of NIFID contain aggregates of α-internexin and neurofilament proteins. Herein, we have shown that: (1) FUS becomes relatively insoluble in NIFID and there are no apparent posttranslational modifications, (2) there are no pathogenic abnormalities in the FUS gene in NIFID, and (3) immunoelectron microscopy demonstrates the fine structural localization of FUS in NIFID which has not previously been described. FUS localized to euchromatin, and strongly with paraspeckles, in nuclei, consistent with its RNA/DNA-binding functions. NCI of varying morphologies were observed. Most frequent were the "loosely aggregated cytoplasmic inclusions," 81% of which had moderate or high levels of FUS immunoreactivity. Much rarer "compact cytoplasmic inclusions" and "tangled twine ball inclusions" were FUS-immunoreactive at their granular peripheries, or heavily FUS-positive throughout, respectively. Thus, FUS may aggregate in the cytoplasm and then admix with neuronal intermediate filament accumulations.

Familial intestinal degenerative neuropathy associated with chronic intestinal pseudo-obstruction

BACKGROUND

Few families with autosomal dominant forms of chronic idiopathic pseudo-obstruction (CIP) have been identified and reported.

METHODS

We compared two families by clinical, laboratory, histopathologic, and genealogical investigations. Ten patients (pts) (five women) from two families, A and B, both with a family history suggesting autosomal dominant CIP, were investigated.

KEY RESULTS

All pts had chronic diarrhea, nine of ten pts had chronic abdominal pain and seven of ten chronic vomiting. Median age for onset of symptoms was 23 (A) and 34 years (B). None had dysphagia, urogenital, neurologic, or ocular symptoms. Small bowel transit and jejunal culture were abnormal in eight of nine. Manometry showed severe jejunal hypomotility in the fasting and fed state and absence of normal phase III in all nine pts and neuropathy-like duodenal alterations in eight of nine. Progress to overt CIP had occurred in six pts. Histopathologic re-evaluation (three pts) showed that criteria of visceral degenerative neuropathy were fulfilled in both families including intranuclear inclusions in all three pts. Genealogic exploration using the unique Swedish Register for Catechetical Meetings disclosed that the two families with all likelihood shared a male ancestor in the 1890 s.

CONCLUSIONS & INFERENCES

The compiled results with striking similarities between family A and B together with genealogy findings indicate that this is one, large kindred with a familial autosomal dominant form of intestinal degenerative neuropathy often progressing to CIP but without extra-intestinal manifestations. This is the fourth and, so far, the largest family reported with these characteristics.

Neuronal intranuclear inclusion disease: two cases of dopa-responsive juvenile parkinsonism with drug-induced dyskinesia

There are very few conditions that present with dopa-responsive juvenile parkinsonism. We present two such children with neuronal intranuclear inclusion disease (NIID) who had an initial good levodopa response that was soon complicated by disabling dopa-induced dyskinesia. One child was diagnosed by rectal biopsy in life, and the other diagnosis was confirmed at postmortem. In this patient, dopamine transporter imaging showed severely decreased binding of the radiotracer in the striatum on both sides. Bilateral subthalamic deep brain stimulation in this patient produced initial improvement, but this was not sustained. Both patients died within 10 years of symptom onset. As well as levodopa responsiveness with rapid onset of dyskinesia, clues to the diagnosis of NIID in patients presenting with parkinsonism include the presence of gaze-evoked nystagmus, early onset dysarthria and dysphagia and oculogyric crises. Differential diagnosis of clinical symptoms and neuropathological findings are discussed including the approach to rectal biopsy for early diagnosis.

ALS-associated fused in sarcoma (FUS) mutations disrupt Transportin-mediated nuclear import

Mutations in fused in sarcoma (FUS) are a cause of familial amyotrophic lateral sclerosis (fALS). Patients carrying point mutations in the C-terminus of FUS show neuronal cytoplasmic FUS-positive inclusions, whereas in healthy controls, FUS is predominantly nuclear. Cytoplasmic FUS inclusions have also been identified in a subset of frontotemporal lobar degeneration (FTLD-FUS). We show that a non-classical PY nuclear localization signal (NLS) in the C-terminus of FUS is necessary for nuclear import. The majority of fALS-associated mutations occur within the NLS and impair nuclear import to a degree that correlates with the age of disease onset. This presents the first case of disease-causing mutations within a PY-NLS. Nuclear import of FUS is dependent on Transportin, and interference with this transport pathway leads to cytoplasmic redistribution and recruitment of FUS into stress granules. Moreover, proteins known to be stress granule markers co-deposit with inclusions in fALS and FTLD-FUS patients, implicating stress granule formation in the pathogenesis of these diseases. We propose that two pathological hits, namely nuclear import defects and cellular stress, are involved in the pathogenesis of FUS-opathies.

Abundant FUS-immunoreactive pathology in neuronal intermediate filament inclusion disease

Neuronal intermediate filament inclusion disease (NIFID) is an uncommon neurodegenerative condition that typically presents as early-onset, sporadic frontotemporal dementia (FTD), associated with a pyramidal and/or extrapyramidal movement disorder. The neuropathology is characterized by frontotemporal lobar degeneration with neuronal inclusions that are immunoreactive for all class IV intermediate filaments (IF), light, medium and heavy neurofilament subunits and alpha-internexin. However, not all the inclusions in NIFID are IF-positive and the primary molecular defect remains uncertain. Mutations in the gene encoding the fused in sarcoma (FUS) protein have recently been identified as a cause of familial amyotrophic lateral sclerosis (ALS). Because of the recognized clinical, genetic and pathological overlap between FTD and ALS, we investigated the possible role of FUS in NIFID. We found abnormal intracellular accumulation of FUS to be a consistent feature of our NIFID cases (n = 5). More neuronal inclusions were labeled using FUS immunohistochemistry than for IF. Several types of inclusions were consistently FUS-positive but IF-negative, including neuronal intranuclear inclusions and glial cytoplasmic inclusions. Double-label immunofluorescence confirmed that many cells had only FUS-positive inclusions and that all cells with IF-positive inclusions also contained pathological FUS. No mutation in the FUS gene was identified in a single case with DNA available. These findings suggest that FUS may play an important role in the pathogenesis of NIFID.

The molecular basis of frontotemporal dementia

Frontotemporal dementia (FTD) is a clinical syndrome with a heterogeneous molecular basis. Familial FTD has been linked to mutations in several genes, including those encoding the microtubule-associated protein tau (MAPT), progranulin (GRN), valosin-containing protein (VCP) and charged multivescicular body protein 2B (CHMP2B). The associated neuropathology is characterised by selective degeneration of the frontal and temporal lobes (frontotemporal lobar degeneration, FTLD), usually with the presence of abnormal intracellular protein accumulations. The current classification of FTLD neuropathology is based on the identity of the predominant protein abnormality, in the belief that this most closely reflects the underlying pathogenic process. Major subgroups include those characterised by the pathological tau, TDP-43, intermediate filaments and a group with cellular inclusions composed of an unidentified ubiquitinated protein. This review will focus on the current understanding of the molecular basis of each of the major FTLD subtypes. It is anticipated that this knowledge will provide the basis of future advances in the diagnosis and treatment of FTD.

Fine structural analysis of the neuronal inclusions of frontotemporal lobar degeneration with TDP-43 proteinopathy

TAR DNA-binding protein of 43 kDa (TDP-43) is a major component of the pathological inclusions of frontotemporal lobar degeneration with TDP-43 proteinopathy, also called FTLD with ubiquitin-positive, tau-negative inclusions (FTLD-U), and motor neuron disease (MND). TDP-43 is predominantly expressed in the nucleus and regulates gene expression and splicing. In FTLD with TDP-43 proteinopathy, neuronal inclusions present variably as cytoplasmic inclusions (NCIs), dystrophic neurites (DNs), and intranuclear inclusions (NIIs), leading to a fourfold neuropathological classification correlating with genotype. There have been few fine structural studies of these inclusions. Thus, we undertook an immunoelectron microscopic study of FTLD with TDP-43 proteinopathy, including sporadic and familial cases with progranulin (GRN) mutation. TDP-43-immunoreactive inclusions comprised two components: granular and filamentous. Filament widths, expressed as mean (range) were: NCI, 9 nm (4-16 nm); DN, 10 nm (5-16 nm); NII, 18 nm (9-50 nm). Morphologically distinct inclusion components may reflect the process of TDP-43 aggregation and interaction with other proteins: determining these latter may contribute towards understanding the heterogeneous pathogenesis of FTLD with TDP-43 proteinopathy.

Atypical frontotemporal lobar degeneration with ubiquitin-positive, TDP-43-negative neuronal inclusions

Frontotemporal lobar degeneration with ubiquitinated inclusions (FTLD-U) is the most common neuropathology associated with the clinical syndrome of frontotemporal dementia (FTD). Recently, TDP-43 was identified as the ubiquitinated pathological protein in both FTLD-U and sporadic amyotrophic lateral sclerosis. Although a number of studies have now confirmed that most sporadic and familial cases of FTLD-U are TDP-43 proteinopathies, there are exceptions. We describe six cases of early onset FTD with FTLD-U pathology that was negative for TDP-43, which we refer to as 'atypical' FTLD-U. All cases were sporadic and had very early onset FTD (mean age = 35 years), characterized by severe progressive psychobehavioural abnormalities in the absence of significant aphasia, cognitive-intellectual dysfunction or motor features. The neuropathological features were highly consistent, with small, round, neuronal cytoplasmic inclusions that were immunoreactive for ubiquitin (ub-ir), but negative for tau, alpha-synuclein, intermediate filaments and TDP-43. Cytoplasmic inclusions were most numerous in the neocortex, dentate granule cells and hippocampal pyramidal neurons. Ub-ir neuronal intra-nuclear inclusions were also present in neocortical and hippocampal neurons and had the unusual appearance of straight, curved or twisted filaments. We believe that these cases represent a new entity that is clinically and pathologically distinct from all currently recognized subtypes of FTLD. Moreover, the existence of such cases indicates that the designations of 'FTLD-U' and 'TDP-43 proteinopathy' should not be considered to be synonymous.

Abnormalities of the nucleus and nuclear inclusions in neurodegenerative disease: a work in progress

Neurodegenerative diseases are characterized pathologically by the abnormal accumulation of pathogenic protein species within the cell. Several neurodegenerative diseases feature intranuclear protein aggregation in the form of intranuclear inclusion bodies. Studies of these intranuclear inclusions are providing important clues regarding the cellular pathophysiology of these diseases, as exemplified by recent progress in defining the genetic basis of a subset of frontotemporal dementia cases. The precise role of intranuclear inclusion bodies in disease pathogenesis is currently a focus of debate. The present review provides an overview of the diverse family of neurodegenerative diseases in which nuclear inclusions form part of the neuropathological spectrum. In addition, current pathogenetic concepts relevant to these diseases will be reviewed and arguments for and against a protective role for intranuclear inclusions will be presented. The relationship of pathological intranuclear inclusions to functional intranuclear bodies will also be discussed. Finally, by analogy with pathological intranuclear inclusions, I will speculate on the possibility that intranuclear protein aggregation may represent a constitutive cellular protective mechanism occurring in neurons under physiological conditions.

Alpha-internexin is structurally and functionally associated with the neurofilament triplet proteins in the mature CNS

Alpha-internexin, a neuronal intermediate filament protein implicated in neurodegenerative disease, coexists with the neurofilament (NF) triplet proteins (NF-L, NF-M, and NF-H) but has an unknown function. The earlier peak expression of alpha-internexin than the triplet during brain development and its ability to form homopolymers, unlike the triplet, which are obligate heteropolymers, have supported a widely held view that alpha-internexin and neurofilament triplet form separate filament systems. Here, we demonstrate, however, that despite a postnatal decline in expression, alpha-internexin is as abundant as the triplet in the adult CNS and exists in a relatively fixed stoichiometry with these subunits. Alpha-internexin exhibits transport and turnover rates identical to those of triplet proteins in optic axons and colocalizes with NF-M on single neurofilaments by immunogold electron microscopy. Alpha-internexin also coassembles with all three neurofilament proteins into a single network of filaments in quadruple-transfected SW13vim(-) cells. Genetically deleting NF-M alone or together with NF-H in mice dramatically reduces alpha-internexin transport and content in axons throughout the CNS. Moreover, deleting alpha-internexin potentiates the effects of NF-M deletion on NF-H and NF-L transport. Finally, overexpressing a NF-H-LacZ fusion protein in mice induces alpha-internexin and neurofilament triplet to aggregate in neuronal perikarya and greatly reduces their transport and content selectively in axons. Our data show that alpha-internexin and the neurofilament proteins are functionally interdependent. The results strongly support the view that alpha-internexin is a fourth subunit of neurofilaments in the adult CNS, providing a basis for its close relationship with neurofilaments in CNS diseases associated with neurofilament accumulation.

Heterogeneous inclusions in neurofilament inclusion disease

Neurofilament inclusion disease (NFID) is a rare disease, whose pathogenesis remains to be elucidated. Immunoreactivity of ubiquitin-binding protein p62 has been reported in various neurodegenerative diseases, but it has not been studied in NFID. In this report we show p62 immunoreactivity in neuronal perikaryon of three cases of NFID. We found inclusions in NFID to be heterogenous based on immunoreactivity for alpha-internexin, phosphorylated neurofilament-H, p62 and ubiquitin. Moreover, we showed both p62- and alpha-internexin-immunoreactive inclusions within the perikarya of the same neuron. Electron microscopy findings support the notion that inclusions in NFID are heterogenous. The present study extends the list of proteins that have been identified as components of neuronal inclusions in NFID, and may help account for the pathogenesis of NFID.

Characterization of Ubiquitinated Intraneuronal Inclusions in a Novel Belgian Frontotemporal Lobar Degeneration Family

The most common histologic feature in patients with frontotemporal lobar degeneration (FTLD) is intracellular brain inclusions of yet uncharacterized proteins that react with antiubiquitin (Ub) antibodies, but not with tau or synuclein (FTLD-U). We identified a four-generation Belgian FTLD family in which 8 patients had dominantly inherited FTLD. In one patient, we showed frontotemporal atrophy with filamentous Ub-positive intracellular inclusions in absence of tau pathology or any alterations in the levels of soluble tau. We characterized the cellular and subcellular localization and morphology of the inclusions. Ub-positive inclusions predominantly occurred within neurons (>97%), but were also observed within oligodendroglia (approximately 2%) and microglia (<1%), but not within astroglia. Regarding the subcellular localization, the intranuclear inclusions (INI) were up to approximately four-fold more frequent than the cytoplasmic inclusions, although the latter were more specific to neurons. The INIs frequently appeared spindle-shaped and 3-dimensional confocal reconstructions identified flattened, leaf-like structures. Ultrastructurally, straight 10- to 18-nm-diameter filaments constituted the spindle-shaped inclusions that occurred in close proximity to the nuclear membrane. Staining for HSP40, p62, and valosin/p97 was observed in only a minority of the inclusions. Whereas the precise nature of the protein remains elusive, characterization of such familial FTLD-U patients would be helpful in identifying a common denominator in the pathogenesis of familial and the more prevalent sporadic FTLD-U.

Pin1 protein associates with neuronal lipofuscin: potential consequences in age-related neurodegeneration

Pin1 protein is a peptidyl-prolyl cis-trans isomerase that modulates the activity of a range of proteins involved in cell function. We and others have demonstrated neuronal Pin1 deficits in Alzheimer's disease (AD) and have shown similar deficits in frontotemporal dementia and in aging. Pin1 may, in fact, be a susceptibility factor; others have shown that Pin1 depletion causes apoptosis in HeLa cells. Further, patterns of AD pathology correlate with regions of lower Pin1 expression in normal human brain; Pin1 knockout mice suffer neurodegeneration; and Pin1 can ameliorate p-tau pathology by isomerizing p-tau, facilitating its trans-specific dephosphorylation and restoring its ability to bind to and restabilize microtubules and thence cytoskeletal integrity. Here, we report a novel localization of high levels of Pin1 with lipofuscin in aging neurons. This association could progressively drain available Pin1 and be deleterious to neuronal function during aging. We also show that Pin1 associates with lipofuscin when lipofuscin accumulations become marked and correlate with susceptibility to neurodegenerative disease. Our data are consistent with the possibility that neuronal Pin1 deficits may be a contributory factor in neurodegeneration associated with aging.