Transcellular spreading of huntingtin aggregates in the Drosophila brain.

A key feature of many neurodegenerative diseases is the accumulation and subsequent aggregation of misfolded proteins. Recent studies have highlighted the transcellular propagation of protein aggregates in several major neurodegenerative diseases, although the precise mechanisms underlying this spreading and how it relates to disease pathology remain unclear. Here we use a polyglutamine-expanded form of human huntingtin (Htt) with a fluorescent tag to monitor the spreading of aggregates in the Drosophila brain in a model of Huntington's disease. Upon expression of this construct in a defined subset of neurons, we demonstrate that protein aggregates accumulate at synaptic terminals and progressively spread throughout the brain. These aggregates are internalized and accumulate within other neurons. We show that Htt aggregates cause non-cell-autonomous pathology, including loss of vulnerable neurons that can be prevented by inhibiting endocytosis in these neurons. Finally we show that the release of aggregates requires N-ethylmalemide-sensitive fusion protein 1, demonstrating that active release and uptake of Htt aggregates are important elements of spreading and disease progression.

Altered nucleosome positioning at the transcription start site and deficient transcriptional initiation in Friedreich ataxia.

Most individuals with Friedreich ataxia (FRDA) are homozygous for an expanded GAA triplet repeat (GAA-TR) mutation in intron 1 of the FXN gene, which results in deficiency of FXN transcript. Consistent with the expanded GAA-TR sequence as a cause of variegated gene silencing, evidence for heterochromatin has been detected in intron 1 in the immediate vicinity of the expanded GAA-TR mutation in FRDA. Transcriptional deficiency in FRDA is thought to result from deficient elongation through the expanded GAA-TR sequence because of repeat-proximal heterochromatin and abnormal DNA structures adopted by the expanded repeat. There is also evidence for deficient transcriptional initiation in FRDA, but its relationship to the expanded GAA-TR mutation remains unclear. We show that repressive chromatin extends from the expanded GAA-TR in intron 1 to the upstream regions of the FXN gene, involving the FXN transcriptional start site. Using a chromatin accessibility assay and a high-resolution nucleosome occupancy assay, we found that the major FXN transcriptional start site, which is normally in a nucleosome-depleted region, is rendered inaccessible by altered nucleosome positioning in FRDA. Consistent with the altered epigenetic landscape the FXN gene promoter, a typical CpG island promoter, was found to be in a transcriptionally non-permissive state in FRDA. Both metabolic labeling of nascent transcripts and an unbiased whole transcriptome analysis revealed a severe deficiency of transcriptional initiation in FRDA. Deficient transcriptional initiation, and not elongation, is the major cause of FXN transcriptional deficiency in FRDA, and it is related to the spread of repressive chromatin from the expanded GAA-TR mutation.

New Perspectives of Gene Therapy on Polyglutamine Spinocerebellar Ataxias: From Molecular Targets to Novel Nanovectors.

Seven of the most frequent spinocerebellar ataxias (SCAs) are caused by a pathological expansion of a cytosine, adenine and guanine (CAG) trinucleotide repeat located in exonic regions of unrelated genes, which in turn leads to the synthesis of polyglutamine (polyQ) proteins. PolyQ proteins are prone to aggregate and form intracellular inclusions, which alter diverse cellular pathways, including transcriptional regulation, protein clearance, calcium homeostasis and apoptosis, ultimately leading to neurodegeneration. At present, treatment for SCAs is limited to symptomatic intervention, and there is no therapeutic approach to prevent or reverse disease progression. This review provides a compilation of the experimental advances obtained in cell-based and animal models toward the development of gene therapy strategies against polyQ SCAs, providing a discussion of their potential application in clinical trials. In the second part, we describe the promising potential of nanotechnology developments to treat polyQ SCA diseases. We describe, in detail, how the design of nanoparticle (NP) systems with different physicochemical and functionalization characteristics has been approached, in order to determine their ability to evade the immune system response and to enhance brain delivery of molecular tools. In the final part of this review, the imminent application of NP-based strategies in clinical trials for the treatment of polyQ SCA diseases is discussed.

Friedreich's ataxia and other hereditary ataxias in Greece: an 18-year perspective.

Limited data exist on the spectrum of heredoataxias in Greece, including the prevalence and phenotype of Friedreich's ataxia (FRDA) and the prevalence and subtypes of dominant spinocerebellar ataxias (SCAs). We analyzed clinically and investigated genetically for FRDA and triplet-repeat expansion SCAs a consecutive series of 186 patients with suspected heredoataxia referred to Athens over 18 years. For prevalence estimates we included patients with molecular diagnosis from Cyprus that were absent from the Athens cohort. The minimum prevalence of FRDA was ~0.9/100,000, with clusters of high prevalence in Aegean islands. FRDA was diagnosed in 73 probands. The genotypic and phenotypic spectrum of FRDA was similar to other populations, with one patient compound heterozygote for a known point mutation in FXN (Asn146Lys). Undiagnosed recessive ataxias included FRDA-like and spastic ataxias. The minimum prevalence of dominant SCAs was ~0.7/100,000. SCA1 (4), SCA7 (4), SCA2, SCA6, and SCA17 (1 each) probands were identified. A molecular diagnosis was reached in 31% of dominant cases. Undiagnosed dominant patients included a majority of type III autosomal dominant cerebellar ataxias. FRDA is the commonest heredoataxia in the Greek population with prevalence towards the lower end of other European populations. Dominant SCAs are almost as prevalent. SCA1, SCA2, SCA6, SCA7 and SCA17 patients complete the spectrum of cases with a specific molecular diagnosis.