Ubiquitin Inclusions Research Articles

Novel Mutations in TARDBP (TDP-43) in Patients with Familial Amyotrophic Lateral Sclerosis

The TAR DNA-binding protein 43 (TDP-43) has been identified as the major disease protein in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitin inclusions (FTLD-U), defining a novel class of neurodegenerative conditions: the TDP-43 proteinopathies. The first pathogenic mutations in the gene encoding TDP-43 (TARDBP) were recently reported in familial and sporadic ALS patients, supporting a direct role for TDP-43 in neurodegeneration. In this study, we report the identification and functional analyses of two novel and one known mutation in TARDBP that we identified as a result of extensive mutation analyses in a cohort of 296 patients with variable neurodegenerative diseases associated with TDP-43 histopathology. Three different heterozygous missense mutations in exon 6 of TARDBP (p.M337V, p.N345K, and p.I383V) were identified in the analysis of 92 familial ALS patients (3.3%), while no mutations were detected in 24 patients with sporadic ALS or 180 patients with other TDP-43–positive neurodegenerative diseases. The presence of p.M337V, p.N345K, and p.I383V was excluded in 825 controls and 652 additional sporadic ALS patients. All three mutations affect highly conserved amino acid residues in the C-terminal part of TDP-43 known to be involved in protein-protein interactions. Biochemical analysis of TDP-43 in ALS patient cell lines revealed a substantial increase in caspase cleaved fragments, including the ∼25 kDa fragment, compared to control cell lines. Our findings support TARDBP mutations as a cause of ALS. Based on the specific C-terminal location of the mutations and the accumulation of a smaller C-terminal fragment, we speculate that TARDBP mutations may cause a toxic gain of function through novel protein interactions or intracellular accumulation of TDP-43 fragments leading to apoptosis.

TDP-43 accumulation in inclusion body myopathy muscle suggests a common pathogenic mechanism with frontotemporal dementia

TAR DNA binding protein-43 (TDP-43) is found in ubiquitinated inclusions (UBIs) in some frontotemporal dementias (FTD-U). One form of FTD-U, due to mutations in the valosin containing protein (VCP) gene,...

Disruption of ubiquitin-mediated processes in diseases of the brain and bone

A role for ubiquitin in the pathogenesis of human diseases was first suggested some two decades ago, from studies that localized the protein to intracellular protein aggregates, which are a feature of the major human neurodegenerative disorders. Although several different mechanisms have been proposed to connect impairment of the UPS (ubiquitin-proteasome system) to the presence of these 'ubiquitin inclusions' within diseased neurones, their significance in the disease process remains to be fully clarified. Ubiquitin inclusions also contain ubiquitin-binding proteins, such as the p62 protein [also known as SQSTM1 (sequestosome 1)], which non-covalently interacts with the ubiquitinated protein aggregates and may serve to mediate their autophagic clearance. p62 is a multifunctional protein and, in the context of bone-resorbing osteoclasts, is an important scaffold in the RANK [receptor activator of NF-kappaB (nuclear factor kappaB)]-NF-kappaB signalling pathway. Further, mutations affecting the UBA domain (ubiquitin-associated domain) of p62 are commonly found in patients with the skeletal disorder PDB (Paget's disease of bone). These mutations impair the ability of p62 to bind to ubiquitin and result in disordered osteoclast NF-kappaB signalling that may underlie the disease aetiology. Recent structural insights into the unusual mechanism of ubiquitin recognition by the p62 UBA domain have helped rationalize the mechanisms by which different PDB mutations exert their negative effects on ubiquitin binding by p62, as well as providing an indication of the ubiquitin-binding selectivity of p62 and, by extension, its normal biological functions.

Sporadic amyotrophic lateral sclerosis: two pathological patterns shown by analysis of distribution of TDP-43-immunoreactive neuronal and glial cytoplasmic inclusions

A nuclear protein, 43-kDa TAR DNA-binding protein (TDP-43), was recently identified as a component of the ubiquitinated inclusions (UIs) in frontotemporal lobar degeneration (FTLD-U) and sporadic amyotrophic lateral sclerosis (SALS). In the present study using immunohistochemistry, we examined various regions of the nervous system in a series of 35 SALS cases using a polyclonal antibody against TDP-43. Seven of the 35 cases had disease durations of more than 10 years with artificial respiratory support (ARS; duration: 69-156 months). In all cases, TDP-43-immunoreactive (ir) neuronal and glial cytoplasmic inclusions (NCIs and GCIs) were found together in many regions, including the histologically affected lower motor neuron nuclei. Cluster analysis of the distribution pattern of TDP-43-ir NCIs for cases without ARS (n = 28) identified two types (type 1, n = 16; type 2, n = 12). Type 2 was distinguished from type 1 by the presence of TDP-43-ir NCIs in the frontotemporal cortex, hippocampal formation, neostriatum and substantia nigra, and was significantly associated with dementia. Eleven of the 28 cases showed UIs in the hippocampal dentate granule cells, all of which had type-2 distribution pattern. Cases with ARS (n = 7) were also classified into the same types (type 1, n = 5; type 2, n = 2). Cases having type-1 distribution pattern (n = 21) showed no evident neuronal loss in most of the non-motor neuron nuclei where TDP-43-ir NCIs were present, whereas cases having type-2 distribution pattern (n = 14) often showed evident neuronal loss in the frontotemporal cortices, amygdaloid nuclei and substantia nigra. These findings indicate that SALS is a multisystem degenerative disease widely affecting both neurons and glial cells with a heterogeneous pattern of TDP-43-ir NCI distribution (SALS showing type-2 distribution pattern being closely linked to FTLD-U), and that long-term survival supported by a respirator has no apparent influence on the TDP-43 neuronal distribution pattern.

TARDBP mutations in amyotrophic lateral sclerosis with TDP-43 neuropathology: a genetic and histopathological analysis

TDP-43 is a major component of the ubiquitinated inclusions that characterise amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) with ubiquitin inclusions (FTLD-U). TDP-43 is an RNA-binding and DNA-binding protein that has many functions and is encoded by the TAR DNA-binding protein gene (TARDBP) on chromosome 1. Our aim was to investigate whether TARDBP is a candidate disease gene for familial ALS that is not associated with mutations in superoxide dismutase 1 (SOD1). TARDBP was sequenced in 259 patients with ALS, FTLD, or both. We used TaqMan-based SNP genotyping to screen for the identified variants in control groups matched to two kindreds of patients for age and ethnic origin. Additional clinical, genetic, and pathological assessments were made in these two families. We identified two variants in TARDBP, which would encode Gly290Ala and Gly298Ser forms of TDP-43, in two kindreds with familial ALS. The variants seem to be pathogenic because they co-segregated with disease in both families, were absent in controls, and were associated with TDP-43 neuropathology in both members of one of these families for whom CNS tissue was available. The Gly290Ala and Gly298Ser mutations are located in the glycine-rich domain of TDP-43, which regulates gene expression and mediates protein-protein interactions such as those with heterogeneous ribonucleoproteins. Owing to the varied and important cellular functions of TDP-43, these mutations might cause neurodegeneration through both gains and losses of function. The finding of pathogenic mutations in TARDBP implicates TDP-43 as an active mediator of neurodegeneration in TDP-43 proteinopathies, a class of disorder that includes ALS and FTLD-U. National Institutes of Health (AG10124, AG17586, AG005136-22, PO1 AG14382), Department of Veterans Affairs, Friedrich-Baur Stiftung (0017/2007), US Public Health Service, ALS Association, and Fundació 'la Caixa'.

RE‐EVALUATION OF ARCHIVAL “DLDH” CASES FOR FRONTOTEMPORAL LOBAR DEGENERATION WITH UBIQUITIN INCLUSIONS: ANTIGEN RETRIEVAL IS ESSENTIAL

The neuropathologic subtypes of frontotemporal lobar degeneration (FTLD) can frequently be differentiated immunohistochemically. The identification of abnormal deposits of tau, ubiquitin, and, more recently, TAR DNA‐binding protein 43 (TDP‐43) and alpha‐internexin may allow separation of neuropathologic subtypes, whereas the lack of staining for these proteins may lead to a diagnosis of “dementia lacking distinctive histology” (DLDH). Because of the importance of accurate pathological diagnosis for the understanding of these disorders, we investigated whether a wider panel of antibodies and more sensitive immunohistochemical methods could allow for better neuropathologic characterization. We undertook a study of 13 autopsy cases with non‐specific diagnoses such as DLDH. We relabeled these brains with antibodies to tau, ubiquitin, TDP‐43, and alpha‐internexin. In addition, we tested the effect of antigen retrieval on the ability to detect the ubiquitin immunolabel. In 7 of the 13 cases, ubiquitin‐immunoreactive inclusions were identified. These cases also immunolabeled with the antibody to TDP‐43. This pattern of staining supported a reclassification to FTLD with ubiquitin inclusions (FTLD‐U). In all of these cases, the antigen retrieval method markedly enhanced ubiquitin immunolabel and was critical for the identification of FTLD‐U pathology. Supported by 1P50‐AG025688.

Autosomal Dominant Subcortical Gliosis Presenting as Frontotemporal Dementia: Clinical and Histopathological Descriptions

We describe a multigenerational kindred with a frontotemporal dementia clinical syndrome (FTDS), extensive subcortical gliosis neuropathology and autosomal dominant genetics. Members of the unique kindred now reported were evaluated at the University of Virginia. Studies were performed in order to establish the likely presence of an underlying neurodegenerative pathogenesis. An extended family tree was assembled. Results from five prospective brain autopsy evaluations and one retrospective brain autopsy were considered. Kindred members affected with this FTDS syndrome have extensive subcortical gliosis capping the frontal horns of the lateral ventricles, evident by neuroradiologic examination. Histopathologic analyses show florid subcortical gliosis, and reveal neither tau nor ubiquitin inclusions. The presence of both maternal and paternal transmission indicate this is an autosomal dominant disorder. Subcortical gliosis in this kindred is either due to mutation of a novel gene, or else represents a unique, previously unrecognized FTDS variant caused by mutation of an already known gene. The kindred is extensive enough to facilitate linkage analysis. Determining the basis of this kindred's autosomal dominant subcortical gliosis could potentially yield mechanistic insight into vascular‐attributed cognitive impairment/dementia syndromes.

Pathological TDP-43 in parkinsonism–dementia complex and amyotrophic lateral sclerosis of Guam

Pathological TDP-43 is the major disease protein in frontotemporal lobar degeneration characterized by ubiquitin inclusions (FTLD-U) with/without motor neuron disease (MND) and in amyotrophic lateral sclerosis (ALS). As Guamanian parkinsonism-dementia complex (PDC) or Guamanian ALS (G-PDC or G-ALS) of the Chamorro population may present clinically similar to FTLD-U and ALS, TDP-43 pathology may be present in the G-PDC and G-ALS. Thus, we examined cortical or spinal cord samples from 54 Guamanian subjects for evidence of TDP-43 pathology. In addition to cortical neurofibrillary and glial tau pathology, G-PDC was associated with cortical TDP-43 positive dystrophic neurites and neuronal and glial inclusions in gray and/or white matter. Biochemical analyses showed the presence of FTLD-U-like insoluble TDP-43 in G-PDC, but not in Guam controls (G-C). Spinal cord pathology of G-PDC or G-ALS was characterized by tau positive tangles as well as TDP-43 positive inclusions in lower motor neurons and glial cells. G-C had variable tau and negligible TDP-43 pathology. These results indicate that G-PDC and G-ALS are associated with pathological TDP-43 similar to FTLD-U with/without MND as well as ALS, and that neocortical or hippocampal TDP-43 pathology distinguishes controls from disease subjects better than tau pathology. Finally, we conclude that the spectrum of TDP-43 proteinopathies should be expanded to include neurodegenerative cognitive and motor diseases, affecting the Chamorro population of Guam.

Co-morbidity of TDP-43 proteinopathy in Lewy body related diseases

Here, we investigated if TAR-DNA-binding protein-43 (TDP-43), the disease protein in frontotemporal lobar degeneration and ubiquitin inclusions with or without motor neuron disease as well as amyotrophic lateral sclerosis, also formed inclusions in Lewy body (LB) disorders including Parkinson's disease (PD) without or with dementia (PDD), and dementia with LBs (DLB) alone or in association with Alzheimer's disease (AD). Immunohistochemical analyses of TDP-43 in clinically well characterized and pathologically confirmed cases of DLB + AD, PD and PDD demonstrated TDP-43 pathology in the following percentage of cases: DLB + AD = 25/80 (31.3%); PD = 5/69 (7.2%); PDD = 4/21 (19%), while DLB and normal controls exhibited no (0/10, 0%) and one cases (1/33, 3%) presenting TDP-43 pathology, respectively. Significant differences in the prevalence of TDP-43 lesions were noted between disease versus normal brains (P < 0.001) as well as demented versus non-demented brains (P < 0.001). Statistical analyses revealed a positive relationship between TDP-43 lesions and several clinical and pathological parameters in these disorders suggesting the TDP-43 pathology may have co-morbid effects in LB diseases. This study expands the concept of TDP-43 proteinopathies by implicating TDP-43 lesions in mechanisms of neurodegeneration in LB disorders.

DJ-1 (PARK7) is associated with 3R and 4R tau neuronal and glial inclusions in neurodegenerative disorders

Mutations in the DJ-1 gene are associated with autosomal recessive Parkinson's disease (PD), but its role in disease pathogenesis is unknown. This study examines DJ-1 immunoreactivity (DJ-1 IR) in a variety of neurodegenerative disorders, Alzheimer's disease (AD), frontotemporal lobar degeneration (FTLD) with Pick bodies, FTLD with MAPT mutations, progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD), in which hyperphosphorylated tau inclusions are the major pathological signature. DJ-1 IR was seen in a subset of neurofibrillary tangles (NFTs), neuropil threads (NTs), and neurites in extracellular plaques in AD; tau inclusions in AD contained both 3R and 4R tau. A subset of Pick bodies in FTLD showed DJ-1 IR. In PSP, DJ-1 IR was present in a few NFTs, NTs and glial cell inclusions. In CBD, DJ-1 IR was seen only in astrocytic plaques. In cases of FTLD with MAPT mutations that were 4R tau positive (i.e. N279K and exon 10+16 mutations), DJ-1 IR was present mostly in oligodendroglial coiled bodies. However, in MAPT R406W mutation cases, DJ-1 IR was associated mainly with NFTs and NTs and these were both 3R and 4R tau positive. No DJ-1 IR was present in FTLD with ubiquitin inclusions (FTLD-U). In AD and FTLD with Pick bodies, DJ-1 protein was enriched in the sarkosyl-insoluble fractions of frozen brain tissue containing insoluble hyperphosphorylated tau, thus strengthening the association of DJ-1 with tau pathology. Additionally using two-dimensional gel electrophoresis, we demonstrated accumulation of acidic pI isoforms of DJ-1 in AD brain, which may compromise its normal function. Our observations confirm previous findings that DJ-1 is present in a subpopulation of glial and neuronal tau inclusions in tau diseases and associated with both 3R and 4R tau isoforms.

A comparative analysis of leucine-rich repeat kinase 2 (Lrrk2) expression in mouse brain and Lewy body disease

Pathogenic substitutions in leucine-rich repeat kinase 2 (LRRK2, Lrrk2) have been genetically linked to familial, late-onset Parkinsonism. End-stage disease is predominantly associated with nigral neuronal loss and Lewy body pathology, but patients may have gliosis, tau or ubiquitin inclusions (pleomorphic pathology). The anatomical distribution of Lrrk2 protein may provide insight into its function in health and neurodegeneration, thus we performed a comparative study with ‘in-house’ and commercially available Lrrk2 antibodies using brain tissue from wild type and human Lrrk2 transgenic bacterial artificial chromosome (BAC) mice, and from diffuse Lewy body disease (DLBD) patients. Lrrk2 protein was ubiquitously expressed and relatively abundant in most brain regions, including the substantia nigra, thalamus and striatum. Lrrk2 was not a major component of Lewy body or neuritic pathology associated with Parkinson’s disease. However, selective loss of dopaminergic neurons in Lrrk2-associated Parkinsonism argues the protein may have regional-specific interactions. Lrrk2 immunohistochemical staining was present in the subventricular zone, a region containing stem cells that give rise to both neurons and glia. A role for Lrrk2 in neurogenesis might provide further insight into the aberrant role of mutant protein in age-associated neurodegeneration with pleomorphic pathology.

TDP-43 in Familial and Sporadic Frontotemporal Lobar Degeneration with Ubiquitin Inclusions

TAR DNA-binding protein 43 (TDP-43) is a major pathological protein of sporadic and familial frontotemporal lobar degeneration with ubiquitin-positive, tau-negative inclusions (FTLD-U) with or without motor neuron disease (MND). Thus, TDP-43 defines a novel class of neurodegenerative diseases called TDP-43 proteinopathies. We performed ubiquitin and TDP-43 immunohistochemistry on 193 cases of familial and sporadic FTLD with or without MND. On selected cases, immunoelectron microscopy and biochemistry were performed. Clinically defined frontotemporal dementias (FTDs) included four groups: 1) familial FTD with mutations in progranulin (n = 36), valosin-containing protein (n = 5), charged multivesicular body protein 2B (n = 4), and linked to chromosome 9p (n = 7); 2) familial cases of FTD with unknown gene association (n = 29); 3) sporadic FTD (n = 72); and 4) familial and sporadic FTD with MND (n = 40). Our studies confirm that the spectrum of TDP-43 proteinopathies includes most cases of sporadic and familial FTLD-U with and without MND and expand this disease spectrum to include reported families with FTD linked to chromosome 9p but not FTD with charged multivesicular body protein 2B mutations. Thus, despite significant clinical, genetic, and neuropathological heterogeneity of FTLD-U, TDP-43 is a common pathological substrate underlying a large subset of these disorders, thereby implicating TDP-43 in novel and unifying mechanisms of FTLD pathogenesis.

A Familial Form of Pallidoluysionigral Degeneration and Amyotrophic Lateral Sclerosis With Divergent Clinical Presentations

We describe a family with a rapidly progressive neurodegenerative disorder characterized by amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) but with unusual neuropathologic features that include pallidoluysionigral degeneration. The proband presented with primary progressive aphasia that evolved into mutism. He subsequently developed dementia with mild disinhibition and parkinsonism and late in the disease showed evidence of motor neuron disease. Two other cases (the proband's mother and maternal uncle) had features of ALS exclusively. All 3 had a young onset (fourth decade) and rapid clinical course, with average time from onset of symptoms to death of 4 years. Postmortem neuropathologic examination of the proband and his uncle showed ALS changes and extensive pallidoluysionigral degeneration without neurofibrillary tangles, ubiquitin inclusions, or detectable abnormalities in the dentate nucleus of the cerebellum. Although this exceptional combination of neuropathologic features has been described in rare cases of sporadic ALS-FTD, no pedigrees have ever been reported. In 2 affected members of this family, we failed to identify mutations in genes associated with weakness, movement disorders, or dementia, including ALS, FTD, selected spinocerebellar ataxias, and Huntington disease. Thus, this disorder may represent a novel autosomal dominantly inherited and rapidly progressive neurodegenerative disorder with a spectrum of clinical presentations but common neuropathologic features.

Anterior opercular syndrome in frontotemporal lobar degeneration with ubiquitin-only immunoreactive neuronal changes

This paper presents for the first time an anterior opercular syndrome in association with a gait disorder, dropped head syndrome, dysphagia, and sialorrhea in a neuropathologically proven case of frontotemporal lobar degeneration with ubiquitin inclusions.

TDP-43 immunoreactivity in neuronal inclusions in familial amyotrophic lateral sclerosis with or without SOD1 gene mutation

Recently, 43-kDa TAR DNA-binding protein (TDP-43) was identified as a component of ubiquitinated inclusions (UIs) in sporadic amyotrophic lateral sclerosis (SALS). To clarify whether TDP-43 immunoreactivity is present in neuronal inclusions in familial ALS (FALS), we examined immunohistochemically the brains and spinal cords from four cases of FALS, two with Cu/Zn superoxide dismutase (SOD1) gene mutation and two without, together with three cases of SALS and three control subjects, using two antibodies, one polyclonal and one monoclonal, against TDP-43. Neuropathologically, the SOD1-related FALS cases were characterized by Lewy body-like hyaline inclusions (LBHIs) in the lower motor neurons. On the other hand, the SOD1-unrelated FALS cases showed degeneration restricted to the upper and lower motor neuron systems, with Bunina bodies (BBs) and UIs in the lower motor neurons, being indistinguishable from SALS. No cytoplasmic TDP-43 immunoreactivity was observed in the control subjects or SOD1-related FALS cases; LBHIs were ubiquitinated, but negative for TDP-43. UIs observed in the SALS and SOD1-unrelated FALS cases were clearly positive for TDP-43. BBs were negative for this protein. Interestingly, in these SALS and FALS cases, glial cells were also found to have cytoplasmic TDP-43-positive inclusions. These findings indicate that the histological and molecular pathology of SALS can occur as a phenotype of FALS without SOD1 mutation.

Frontotemporal Dementia

Frontotemporal dementia (FTD) is an uncommon but important form of degenerative disease. It may make up 50% of dementia cases presenting before age 60. The symptoms are related to the anatomic areas affected. Neary divided the clinical syndromes into "frontotemporal dementia," "progressive nonfluent aphasia," and "semantic dementia." However, the pathology may extend beyond the frontal and temporal lobes and additional symptoms may be found. Although most cases are sporadic, some cases are genetic. The best-known genetic mutation causing FTD is frontotemporal dementia with parkinsonism, linked to the microtubule-associated protein tau on chromosome 17. There are other known genes and chromosome loci related to FTD. The most common pathology found is frontotemporal degeneration with ubiquitin inclusions. In contrast, FTD with Pick bodies is rare. Although there are strategies to help patients and their families, there is no known treatment for the disease.

Progranulin mutations in Dutch familial frontotemporal lobar degeneration

Mutations in the progranulin (PGRN) gene have recently been identified in frontotemporal lobar degeneration with ubiquitin inclusions linked to chromosome 17q21. We report here the finding of two novel frameshift mutations and three possible pathogenic missense mutations in the PGRN gene. Furthermore, we determined the frequency of PGRN mutations in familial cases recruited from a large population-based study of frontotemporal lobar degeneration carried out in The Netherlands.

Frontotemporal Lobar Degeneration: Current Concepts in the Light of Recent Advances

Work done over the past decade has led to a molecular understanding of frontotemporal lobar degeneration (FTLD), a deadly disease that afflicts patients in mid-life. It is a common cause of dementia, second only to Alzheimer's disease in the population below 65 years of age. Neuroanatomical and neurobiological substrates have been identified for the three major subtypes of FTLD and these discoveries have broadened the FTLD spectrum to include amyotrophic lateral sclerosis (ALS). Mutations in MAPT were found to cause frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), a familial disorder with filamentous tau inclusions in nerve cells and glial cells. FTDP-17 can result in clinical syndromes that closely resemble progressive supranuclear palsy, corticobasal degeneration and Pick's disease. More recently, mutations in three genes (VCP, CHMP2B and PGRN) have been found to cause FTLD with ubiquitin-positive, tau-negative neuronal inclusions (FTLD-U). They explain a large proportion of inherited FTLD-U. It remains to be seen whether dementia lacking distinctive histopathology (DLDH) constitutes a third disease category, as many of these cases are now being reclassified as FTLD-U. Recently, TAR DNA-binding protein-43 (TDP-43) has been identified as a key protein of the ubiquitin inclusions of FTLD-U and ALS. Thus, for familial forms of FTLD and related disorders, we now know the primary etiologies and accumulating proteins. These findings are pivotal for dissecting the pathways by which different etiologies lead to the varied clinicopathological presentations of FTLD.

Progranulin Mutations in Ubiquitin-Positive Frontotemporal Dementia Linked to Chromosome 17q21

Two genetically distinct types of frontotemporal dementia (FTD) are linked to chromosome 17q21. FTD with parkinsonism (FTDP-17) results from mutations in the gene encoding microtubule associated protein tau (MAPT) and is associated with tau deposition in the patient's brain. An increasing number of FTD families are linked to 17q21 in the absence of a demonstrable MAPT mutation. Brains of these patients do not show tau deposits, but tau-negative intra- and perinuclear inclusions of unknown composition that are immunoreactive to ubiquitin (FTDU-17). These ubiquitin inclusions are located in the cytoplasm or nucleus of predominantly neuronal cells of affected brain regions. By extensive segregation analyses in conclusively linked FTDU-17 families, the candidate region was reduced to a 6.2 Mb segment containing MAPT; however, genomic sequencing of MAPT in FTDU-17 patients excluded disease-causing mutations. Further, the linked region was characterized by the presence of multiple low-copy repeat regions associated with genomic instability. However, we excluded genomic rearrangements as the cause of FTDU-17. Subsequent sequencing of positional candidate genes identified loss-of-function mutations in the gene encoding progranulin (PGRN), a growth factor involved in multiple physiological processes such as cellular proliferation and survival and tissue repair, and pathological processes including tumorigenesis. In a Belgian FTD patient series, the prevalence of PGRN mutations was 3.5 times higher than that of MAPT mutations underscoring a major role for PGRN in FTD pathogenesis. Together, mutation data provided convincing evidence that PGRN haploinsufficiency leads to neurodegeneration because of reduced PGRN-mediated neuronal survival. The PGRN protein is not deposited in the ubiquitin-positive inclusions, the nature of which remains unknown. Due to the functions of PGRN in neuronal survival and the clinicopathological overlaps between FTD and other dementias it is likely that reduced PGRN expression is associated with the progression of other neurodegenerative brain diseases including Alzheimer's disease. These findings open promising novel targets for therapeutic intervention against neurodegeneration.

Convergent Roles of α‐Synuclein, DA Metabolism, and the Ubiquitin‐Proteasome System in Nigrostriatal Toxicity

Recent studies disclosed the relevance of specific molecules for the onset of Parkinson's disease (PD) and for the composition of neuronal inclusions. The scenario which is now emerging leads to identify a potential common pathway named the ubiquitin-proteasome (UP) system. In line with this, striatal or systemic inhibiton of the UP system causes experimental Parkinsonism characterized by the formation of neuronal inclusions. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which is also a complex I inhibitor, has been used for decades to produce experimental Parkinsonism with no evidence for neuronal inclusions in rodents. This leaves open the question whether neuronal inclusions need an alternative mechanism or the inhibition of complex I needs to be carried out continuously to build up inclusions. In the present article, we administered continuously MPTP. In these experimental conditions we compared the neurological consequence of intermittent versus continuous MPTP. In both cases we observed a severe dopamine (DA) denervation and cell loss. However, when MPTP was delivered continuously, spared DA nigral neurons develop ubiquitin, parkin, and alpha-synuclein positive inclusions, which are not detectable after intermittent dosing. The onset of Parkinsonism is associated with inhibition of the UP system. We compared these results with those obtained with amphetamine derivative in vivo and in vitro in which occurrence of neuronal inclusions was associated with inhibition of the UP system and we evaluated the role of DA metabolism in inducing these effects.