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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 dosedependent degeneration of cortical and spinal motor neurons and development of spastic quadriplegia reminiscent of ALS. A dosedependent 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.A myotrophic lateral sclerosis (ALS) is one of the most common progressive neuromuscular diseases worldwide and is characterized by degeneration of cortical motor neurons, the motor nuclei of the brainstem, and the anterior horn cells of the spinal cord. Dysfunction and death of these neurons lead to muscle weakness, atrophy, and spasticity (1). Frontotemporal lobar degeneration (FTLD) is the second most common form of cortical dementia in the presenium, accounting for ≈20% of dementia patients in this age group (2). Both ALS and FTLD patients are characterized by ubiquitinated neuronal cytoplasmic and intranuclear inclusions (NCIs and NIIs) in affected brain regions (2). Approximately 20% of patients with ALS show frontal lobe dysfunction that overlaps with the pathology of FTLD, suggesting that FTLD and ALS are part of the same disease spectrum (3).The recent identification of the TAR DNA-binding protein-43 (TDP-43) as a major protein constituent of NCIs and NIIs in ALS and FTLD (FTLD-U or FTLD-TDP) patients has offered a molecular link between these two disorders (4, 5). TDP-43 is a 414-amino acid protein with two highly conserved RNA recognition motifs (RRM1 and RRM2), a nuclear localization signal (NLS) at the protein N-terminus, and a glycine-rich region mediating protein-protein interactions at the C-terminus (6-9). Pathological TDP-43 is abnormally ubiquitinated, hyperphosphorylated, and N-terminally cleaved to generate CTFs (4, 5).Missense mutations in the TDP-43 gene (TARDBP), mostly in the C-terminal glycine-rich region, have been identified in patients wi...

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.

Amyloid-beta (Abeta) 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 Abeta-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 Abeta42-depositing BRI-Abeta42 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 ( approximately 8-fold increased) and APPPS1 ( approximately 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.

The current study, although small-scale, suggests increased DKI metrics, in the absence of alterations in diffusion tensor imaging metrics in the cortex and thalamus of APP/presenilin 1 mice with established amyloidosis. These results warrant further investigations on the potential of DKI as a sensitive marker for Alzheimer's disease.

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preclinical diagnosis for ethical reasons, and to the possibility of using "conversion to dementia" as a gold standard for diagnosis (in the lack of pathology data). The resulting 5 sequential phases were: 1) pilot studies, 2) clinical assay development for clinical disease, 3) prospective longitudinal repository studies, 4) prospective diagnostic studies, and 5) disease control studies (Table). Because of the required adaptations, biomarkers for AD can be used for biomarker-based diagnoses and not yet for screening purposes. Conclusions: The adaptation of the oncology framework to AD aims to systematize the validation of AD biomarkers. The important limitations restrict the generalizability of results to the general population and the use of such biomarkers for screening purposes. This initiative should be considered as a first, although necessary, step to the definition of a systematic validation of biomarkers for AD.