Ivy Cuijt

Null mutations in progranulin cause ubiquitin-positive frontotemporal dementia linked to chromosome 17q21.

Frontotemporal dementia (FTD) with ubiquitin-immunoreactive neuronal inclusions (both cytoplasmic and nuclear) of unknown nature has been linked to a chromosome 17q21 region (FTDU-17) containing MAPT (microtubule-associated protein tau). FTDU-17 patients have consistently been shown to lack a tau-immunoreactive pathology, a feature characteristic of FTD with parkinsonism linked to mutations in MAPT (FTDP-17). Furthermore, in FTDU-17 patients, mutations in MAPT and genomic rearrangements in the MAPT region have been excluded by both genomic sequencing and fluorescence in situ hybridization on mechanically stretched chromosomes. Here we demonstrate that FTDU-17 is caused by mutations in the gene coding for progranulin (PGRN), a growth factor involved in multiple physiological and pathological processes including tumorigenesis. Besides the production of truncated PGRN proteins due to premature stop codons, we identified a mutation within the splice donor site of intron 0 (IVS0 + 5G > C), indicating loss of the mutant transcript by nuclear degradation. The finding was made within an extensively documented Belgian FTDU-17 founder family. Transcript and protein analyses confirmed the absence of the mutant allele and a reduction in the expression of PGRN. We also identified a mutation (c.3G > A) in the Met1 translation initiation codon, indicating loss of PGRN due to lack of translation of the mutant allele. Our data provide evidence that PGRN haploinsufficiency leads to neurodegeneration because of reduced PGRN-mediated neuronal survival. Furthermore, in a Belgian series of familial FTD patients, PGRN mutations were 3.5 times more frequent than mutations in MAPT, underscoring a principal involvement of PGRN in FTD pathogenesis.

A C9orf72 promoter repeat expansion in a Flanders-Belgian cohort with disorders of the frontotemporal lobar degeneration-amyotrophic lateral sclerosis spectrum: a gene identification study

BACKGROUND Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are extremes of a clinically, pathologically, and genetically overlapping disease spectrum. A locus on chromosome 9p21 has been associated with both disorders, and we aimed to identify the causal gene within this region. METHODS We studied 305 patients with FTLD, 137 with ALS, and 23 with concomitant FTLD and ALS (FTLD-ALS) and 856 controls from Flanders (Belgium); patients were identified from a hospital-based cohort and were negative for mutations in known FTLD and ALS genes. We also examined the family of one patient with FTLD-ALS previously linked to 9p21 (family DR14). We analysed 130 kbp at 9p21 in association and segregation studies, genomic sequencing, repeat genotyping, and expression studies to identify the causal mutation. We compared genotype-phenotype correlations between mutation carriers and non-carriers. FINDINGS In the patient-control cohort, the single-nucleotide polymorphism rs28140707 within the 130 kbp region of 9p21 was associated with disease (odds ratio [OR] 2·6, 95% CI 1·5-4·7; p=0·001). A GGGGCC repeat expansion in C9orf72 completely co-segregated with disease in family DR14. The association of rs28140707 with disease in the patient-control cohort was abolished when we excluded GGGGCC repeat expansion carriers. In patients with familial disease, six (86%) of seven with FTLD-ALS, seven (47%) of 15 with ALS, and 12 (16%) of 75 with FTLD had the repeat expansion. In patients without known familial disease, one (6%) of 16 with FTLD-ALS, six (5%) of 122 with ALS, and nine (4%) of 230 with FTLD had the repeat expansion. Mutation carriers primarily presented with classic ALS (10 of 11 individuals) or behavioural variant FTLD (14 of 15 individuals). Mean age at onset of FTLD was 55·3 years (SD 8·4) in 21 mutation carriers and 63·2 years (9·6) in 284 non-carriers (p=0·001); mean age at onset of ALS was 54·5 years (9·9) in 13 carriers and 60·4 years (11·4) in 124 non-carriers. Postmortem neuropathological analysis of the brains of three mutation carriers with FTLD showed a notably low TDP-43 load. In brain at postmortem, C9orf72 expression was reduced by nearly 50% in two carriers compared with nine controls (p=0·034). In familial patients, 14% of FTLD-ALS, 50% of ALS, and 62% of FTLD was not accounted for by known disease genes. INTERPRETATION We identified a pathogenic GGGGCC repeat expansion in C9orf72 on chromosome 9p21, as recently also reported in two other studies. The GGGGCC repeat expansion is highly penetrant, explaining all of the contribution of chromosome 9p21 to FTLD and ALS in the Flanders-Belgian cohort. Decreased expression of C9orf72 in brain suggests haploinsufficiency as an underlying disease mechanism. Unidentified genes probably also contribute to the FTLD-ALS disease spectrum. FUNDING Full funding sources listed at end of paper (see Acknowledgments).

TDP-43 transgenic mice develop spastic paralysis and neuronal inclusions characteristic of ALS and frontotemporal lobar degeneration.

Neuronal cytoplasmic and intranuclear aggregates of RNA-binding protein TDP-43 are a hallmark feature of neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). ALS and FTLD show a considerable clinical and pathological overlap and occur as both familial and sporadic forms. Though missense mutations in TDP-43 cause rare forms of familial ALS, it is not yet known whether this is due to loss of TDP-43 function or gain of aberrant function. Moreover, the role of wild-type (WT) TDP-43, associated with the majority of familial and sporadic ALS/FTLD patients, is also currently unknown. Generating homozygous and hemizygous WT human TDP-43 transgenic mouse lines, we show here a dose-dependent degeneration of cortical and spinal motor neurons and development of spastic quadriplegia reminiscent of ALS. A dose-dependent degeneration of nonmotor cortical and subcortical neurons characteristic of FTLD was also observed. Neurons in the affected spinal cord and brain regions showed accumulation of TDP-43 nuclear and cytoplasmic aggregates that were both ubiquitinated and phosphorylated as observed in ALS/FTLD patients. Moreover, the characteristic ≈25-kDa C-terminal fragments (CTFs) were also recovered from nuclear fractions and correlated with disease development and progression in WT TDP-43 mice. These findings suggest that ≈25-kDa TDP-43 CTFs are noxious to neurons by a gain of aberrant nuclear function.

Drosophila screen connects nuclear transport genes to DPR pathology in c9ALS/FTD

Hexanucleotide repeat expansions in C9orf72 are the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal degeneration (FTD) (c9ALS/FTD). Unconventional translation of these repeats produces dipeptide repeat proteins (DPRs) that may cause neurodegeneration. We performed a modifier screen in Drosophila and discovered a critical role for importins and exportins, Ran-GTP cycle regulators, nuclear pore components, and arginine methylases in mediating DPR toxicity. These findings provide evidence for an important role for nucleocytoplasmic transport in the pathogenic mechanism of c9ALS/FTD.

Cellular ageing, increased mortality and FTLD-TDP-associated neuropathology in progranulin knockout mice†

Loss‐of‐function mutations in progranulin (GRN) are associated with frontotemporal lobar degeneration with intraneuronal ubiquitinated protein accumulations composed primarily of hyperphosphorylated TDP‐43 (FTLD‐TDP). The mechanism by which GRN deficiency causes TDP‐43 pathology or neurodegeneration remains elusive. To explore the role of GRN in vivo, we established Grn knockout mice using a targeted genomic recombination approach and Cre‐LoxP technology. Constitutive Grn homozygous knockout (Grn−/−) mice were born in an expected Mendelian pattern of inheritance and showed no phenotypic alterations compared to heterozygous (Grn+/−) or wild‐type (Wt) littermates until 10 months of age. From then, Grn−/− mice showed reduced survival accompanied by significantly increased gliosis and ubiquitin‐positive accumulations in the cortex, hippocampus, and subcortical regions. Although phosphorylated TDP‐43 could not be detected in the ubiquitinated inclusions, elevated levels of hyperphosphorylated full‐length TDP‐43 were recovered from detergent‐insoluble brain fractions of Grn−/− mice. Phosphorylated TDP‐43 increased with age and was primarily extracted from the nuclear fraction. Grn−/− mice also showed degenerative liver changes and cathepsin D‐positive foamy histiocytes within sinusoids, suggesting widespread defects in lysosomal turnover. An increase in insulin‐like growth factor (IGF)‐1 was observed in Grn−/− brains, and increased IGF‐1 signalling has been associated with decreased longevity. Our data suggest that progranulin deficiency in mice leads to reduced survival in adulthood and increased cellular ageing accompanied by hyperphosphorylation of TDP‐43, and recapitulates key aspects of FTLD‐TDP neuropathology. Copyright

Intraneuronal amyloid β and reduced brain volume in a novel APP T714I mouse model for Alzheimer's disease

Transgenic mouse models of Alzheimers disease (AD) expressing high levels of amyloid precursor protein (APP) with familial AD (FAD) mutations have proven to be extremely useful in understanding pathogenic processes of AD especially those that involve amyloidogenesis. We earlier described Austrian APP T714I pathology that leads to one of the earliest AD age-at-onsets with abundant intracellular and extracellular amyloid deposits in brain. The latter strikingly was non-fibrillar diffuse amyloid, composed of N-truncated A beta 42 in absence of A beta 40. In vitro, this mutation leads to one of the highest A beta 42/A beta 40 ratios among all FAD mutations. We generated an APP T714I transgenic mouse model that despite having 10 times lower transgene than endogenous murine APP deposited intraneuronal A beta in brain by 6 months of age. Accumulations increased with age, and this was paralleled by decreased brain sizes on volumetric MRI, compared to age-matched and similar transgene-expressing APP wild-type mice, although, with these levels of transgenic expression we did not detect neuronal loss or significant memory impairment. Immunohistochemical studies revealed that the majority of the intraneuronal A beta deposits colocalized with late endosomal markers, although some A beta inclusions were also positive for lysosomal and Golgi markers. These data support earlier observations of A beta accumulation in the endosomal-lysosomal pathway and the hypothesis that intraneuronal accumulation of A beta could be an important factor in the AD pathogenesis.

Progranulin expression correlates with dense-core amyloid plaque burden in Alzheimer disease mouse models.

Amyloid‐β (Aβ) plaques are pathological hallmarks of Alzheimer disease (AD). In addition, innate inflammatory responses, such as those mediated by microglia, are integral to the pathogenesis of AD. Interestingly, only dense‐core plaques and not diffuse plaques are associated with neuritic and inflammatory pathology in AD patients as well as in mouse AD models. However, the precise neuropathological changes that occur in the brain in response to amyloid deposition are largely unknown. To study the molecular mechanism(s) responsible for Aβ‐mediated neuropathology, we performed a gene expression analysis on laser‐microdissected brain tissue of Tg2576 and APPPS1 mice that are characterized by different types of amyloid plaques and genetic backgrounds. Data were validated by image and biochemical analyses on different ages of Tg2576, APPPS1, and Aβ42‐depositing BRI‐Aβ42 mice. Consistent with an important role of inflammatory responses in AD, we identified progranulin (mouse Grn; human GRN) as one of the top ten up‐regulated molecules in Tg2576 (≈8‐fold increased) and APPPS1 (≈2‐fold increased) mice compared to littermate controls, and among the eight significantly up‐regulated molecules common to both mouse models. In addition, Grn levels correlated significantly with amyloid load, especially the dense‐core plaque pathology (p < 0.001). We further showed that Grn is up‐regulated in microglia and neurons and neurites around dense‐core plaques, but not in astrocytes or oligodendrocytes, as has been shown in AD patients. Our data therefore support the ongoing use of these mouse models in drug trials, especially those with anti‐inflammatory compounds. Moreover, the correlation of Grn with increasing disease severity in AD mouse models prompts human studies exploring the viability of GRN as a disease biomarker. Because loss of GRN has recently been shown to cause frontotemporal dementia and serves as a risk factor for AD, the strong GRN reactivity around dense‐core plaques is consistent with an important role of this factor in AD pathogenesis. Copyright

Loss of TBK1 is a frequent cause of frontotemporal dementia in a Belgian cohort

Objective: To assess the genetic contribution of TBK1, a gene implicated in amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and FTD-ALS, in Belgian FTD and ALS patient cohorts containing a significant part of genetically unresolved patients. Methods: We sequenced TBK1 in a hospital-based cohort of 482 unrelated patients with FTD and FTD-ALS and 147 patients with ALS and an extended Belgian FTD-ALS family DR158. We followed up mutation carriers by segregation studies, transcript and protein expression analysis, and immunohistochemistry. Results: We identified 11 patients carrying a loss-of-function (LOF) mutation resulting in an overall mutation frequency of 1.7% (11/629), 1.1% in patients with FTD (5/460), 3.4% in patients with ALS (5/147), and 4.5% in patients with FTD-ALS (1/22). We found 1 LOF mutation, p.Glu643del, in 6 unrelated patients segregating with disease in family DR158. Of 2 mutation carriers, brain and spinal cord was characterized by TDP-43-positive pathology. The LOF mutations including the p.Glu643del mutation led to loss of transcript or protein in blood and brain. Conclusions: TBK1 LOF mutations are the third most frequent cause of clinical FTD in the Belgian clinically based patient cohort, after C9orf72 and GRN, and the second most common cause of clinical ALS after C9orf72. These findings reinforce that FTD and ALS belong to the same disease continuum.

Identification of 2 Loci at Chromosomes 9 and 14 in a Multiplex Family With Frontotemporal Lobar Degeneration and Amyotrophic Lateral Sclerosis

BACKGROUND Frontotemporal lobar degeneration (FTLD) is a neurodegenerative brain disorder that can be accompanied by signs of amyotrophic lateral sclerosis (ALS). OBJECTIVE To identify a novel gene for FTLD-ALS. DESIGN Genome-wide linkage study in a multiplex family with FTLD-ALS with subsequent fine mapping and mutation analyses. SETTING Memory Clinic of the Middelheim General Hospital. PATIENTS An extended Belgian family with autosomal dominant FTLD-ALS, DR14, with a mean age at onset of 58.1 years (range, 51-65 years [n = 9]) and mean disease duration of 6.4 years (range, 1-17 years [n = 9]). The proband with clinical FTLD showed typical FTLD pathology with neuronal ubiquitin-immunoreactive inclusions that were positive for the transactivation response DNA-binding protein 43 (TDP-43). MAIN OUTCOME MEASURE Linkage to chromosome 9 and 14. RESULTS We found significant linkage to chromosome 9p23-q21 (multipoint logarithm of odds [LOD] score = 3.38) overlapping with a known FTLD-ALS locus (ALSFTD2) and nearly significant linkage to a second locus at chromosome 14q31-q32 (multipoint LOD score = 2.79). Obligate meiotic recombinants defined candidate regions of 74.7 megabase pairs (Mb) at chromosome 9 and 14.6 Mb near the telomere of chromosome 14q. In both loci, the disease haplotype segregated in all patients in the family. Mutation analysis of selected genes and copy number variation analysis in both loci did not reveal segregating pathogenic mutations. CONCLUSIONS Family DR14 provides additional significant evidence for the importance of the chromosome 9 gene to FTLD-ALS and reveals a possible novel locus for FTLD-ALS at chromosome 14. The identification of the underlying genetic defect(s) will significantly contribute to the understanding of neurodegenerative disease mechanisms in FTLD, ALS, and associated neurodegenerative disorders.

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.