Review: Recent progress in frontotemporal lobar degeneration

Increased metal content in the TDP-43(A315T) transgenic mouse model of frontotemporal lobar degeneration and amyotrophic lateral sclerosis

Disrupted metal homeostasis is a consistent feature of neurodegenerative disease in humans and is recapitulated in mouse models of Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis (ALS) and neuronal ceriod lipofuscinosis. While the definitive pathogenesis of neurodegenerative disease in humans remains to be fully elucidated, disease-like symptoms in the mouse models are all driven by the presence or over-expression of a putative pathogenic protein, indicating an in vivo relationship between expression of these proteins, disrupted metal homeostasis and the symptoms of neuronal failure. Recently it was established that mutant TAR DNA binding protein-43 (TDP-43) is associated with the development of frontotemporal lobar degeneration and ALS. Subsequent development of transgenic mice that express human TDP-43 carrying the disease-causing A315T mutation has provided new opportunity to study the underlying mechanisms of TDP-43-related neurodegenerative disease. We assessed the cognitive and locomotive phenotype of TDP-43 (A315T) mice and their wild-type littermates and also assessed bulk metal content of brain and spinal cord tissues. Metal levels in the brain were not affected by the expression of mutant TDP-43, but zinc, copper, and manganese levels were all increased in the spinal cords of TDP-43 (A315T) mice when compared to wild-type littermates. Performance of the TDP-43 (A315T) mice in the Y-maze test for cognitive function was not significantly different to wild-type mice. By contrast, performance of the TDP-43 (A315T) in the rotarod test for locomotive function was consistently worse than wild-type mice. These preliminary in vivo data are the first to show that expression of a disease-causing form of TDP-43 is sufficient to disrupt metal ion homeostasis in the central nervous system. Disrupted metal ion homeostasis in the spinal cord but not the brain may explain why the TDP-43 (A315T) mice show symptoms of locomotive decline and not cognitive decline.

Histone deacetylase class II and acetylated core histone immunohistochemistry in human brains with Huntington's disease

BACKGROUND AND OBJECTIVE

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder, caused by a CAG/polyglutamine repeat expansion, which is associated with a dysregulation of histone function and an impairment of protein transcription. Histone deacetylase (HDAC) inhibitors, such as vorinostat (SAHA), have shown promise as therapeutic agents. However, there have been few studies on the expression of HDACs and acetylated core histones (AcHs) in either normal animals or humans, or in HD patients or HD animal models. Therefore, we investigated the expression of HDACs and AcHs in HD brain by immunohistochemistry, and have compared findings with elderly control subjects and patients with frontotemporal lobar degeneration (FTLD) to determine whether any observed changes were specific for HD.

RESULTS AND CONCLUSION

we show specific and significant losses of AcH2A, AcH2B, AcH3 and AcH4 expression from cells in the caudate nucleus and Purkinje cells of the cerebellum in HD compared to patients with FTLD and control subjects, while the level of HDAC 5 was increased in these cells.

Frontotemporal dementias: Recent advances and current controversies

Frontotemporal dementia (FTD) syndromes comprise a heterogeneous group of neurodegenerative conditions characterized by atrophy in the frontal and temporal lobes. Three main clinical variants are recognized: Behavioral variant (bv-FTD), Semantic dementia (SD), and Progressive nonfluent aphasia (PNFA). However, logopenic/phonological (LPA) variant has been recently described, showing a distinctive pattern of brain atrophy and often associated to Alzheimer's disease pathology. The diagnosis of FTD is challenging, since there is clinical, pathological, and genetic overlap between the variants and other neurodegenerative diseases, such as motoneuron disease (MND) and corticobasal degeneration (CBD). In addition, patients with gene mutations (tau and progranulin) display an inconsistent clinical phenotype and the correspondence between the clinical variant and its pathology is unpredictable. New cognitive tests based on social cognition and emotional recognition together with advances in molecular pathology and genetics have contributed to an improved understanding. There is now a real possibility of accurate biomarkers for early diagnosis. The present review concentrates on new insights and debates in FTD.

TDP-43 autoregulation: implications for disease

TDP-43 is a nuclear protein that has been shown to play a central role in RNA metabolism. In recent years, this protein has become very important in the study of neurodegenerative diseases such as amyotrophic lateral sclerosis and frontotemporal lobar degeneration (FTLD). These diseases share, as common feature, the presence of abnormally aggregated, posttranslationally modified, and mislocalized TDP-43 in the cell cytoplasm of both neurons and glial cells. A major question in TDP-43 research is represented by the investigation of the mechanism(s) that trigger this process and its potential consequences. Regarding the first issue, it is likely that relative protein expression levels might play an important role as has been demonstrated for many protein aggregation processes. In fact, the eventual misregulation of TDP-43 expression leading to enhanced protein production might well correlate with enhanced aggregation, and thus results in increasingly harmful gain- or loss-of-function effects on cellular metabolism. For this reason, it is important to determine the mechanisms that act to regulate TDP-43 levels within the cell. In normal conditions, it is now clear that TDP-43 can modulate its own protein levels through a negative feedback loop triggered by binding to its own RNA in the 3'UTR region leading to mRNA degradation. This work discusses how an eventual disruption of this mechanism might affect TDP-43 pathology, focusing in particular on its association with stress granules and intrinsic aggregation properties.

Parkinson's disease: genetics and pathogenesis

Recent investigation into the mechanisms of Parkinson's disease (PD) has generated remarkable insight while simultaneously challenging traditional conceptual frameworks. Although the disease remains defined clinically by its cardinal motor manifestations and pathologically by midbrain dopaminergic cell loss in association with Lewy bodies, it is now recognized that PD has substantially more widespread impact, causing a host of nonmotor symptoms and associated pathology in multiple regions throughout the nervous system. Further, the discovery and validation of PD-susceptibility genes contradict the historical view that environmental factors predominate, and blur distinctions between familial and sporadic disease. Genetic advances have also promoted the development of improved animal models, highlighted responsible molecular pathways, and revealed mechanistic overlap with other neurodegenerative disorders. In this review, we synthesize emerging lessons on PD pathogenesis from clinical, pathological, and genetic studies toward a unified concept of the disorder that may accelerate the design and testing of the next generation of PD therapies.