Altered H3 histone acetylation impairs high-fidelity DNA repair to promote cerebellar degeneration in spinocerebellar ataxia type 7.

A common mechanism in inherited ataxia is a vulnerability of DNA damage. Spinocerebellar ataxia type 7 (SCA7) is a CAG-polyglutamine-repeat disorder characterized by cerebellar and retinal degeneration. Polyglutamine-expanded ataxin-7 protein incorporates into STAGA co-activator complex and interferes with transcription by altering histone acetylation. We performed chromatic immunoprecipitation sequencing ChIP-seq on cerebellum from SCA7 mice and observed increased H3K9-promoter acetylation in DNA repair genes, resulting in increased expression. After detecting increased DNA damage in SCA7 cells, mouse primary cerebellar neurons, and patient stem-cell-derived neurons, we documented reduced homology-directed repair (HDR) and single-strand annealing (SSA). To evaluate repair at endogenous DNA in native chromosome context, we modified linear amplification-mediated high-throughput genome-wide translocation sequencing and found that DNA translocations are less frequent in SCA7 models, consistent with decreased HDR and SSA. Altered DNA repair function in SCA7 may predispose the subject to excessive DNA damage, leading to neuron demise and highlights DNA repair as a therapy target.

Metabolic and Organelle Morphology Defects in Mice and Human Patients Define Spinocerebellar Ataxia Type 7 as a Mitochondrial Disease.

Spinocerebellar ataxia type 7 (SCA7) is a retinal-cerebellar degenerative disorder caused by CAG-polyglutamine (polyQ) repeat expansions in the ataxin-7 gene. As many SCA7 clinical phenotypes occur in mitochondrial disorders, and magnetic resonance spectroscopy of patients revealed altered energy metabolism, we considered a role for mitochondrial dysfunction. Studies of SCA7 mice uncovered marked impairments in oxygen consumption and respiratory exchange. When we examined cerebellar Purkinje cells in mice, we observed mitochondrial network abnormalities, with enlarged mitochondria upon ultrastructural analysis. We developed stem cell models from patients and created stem cell knockout rescue systems, documenting mitochondrial morphology defects, impaired oxidative metabolism, and reduced expression of nicotinamide adenine dinucleotide (NAD+) production enzymes in SCA7 models. We observed NAD+ reductions in mitochondria of SCA7 patient NPCs using ratiometric fluorescent sensors and documented alterations in tryptophan-kynurenine metabolism in patients. Our results indicate that mitochondrial dysfunction, stemming from decreased NAD+, is a defining feature of SCA7.

Modeling simple repeat expansion diseases with iPSC technology.

A number of human genetic disorders, including Huntington's disease, myotonic dystrophy type 1, C9ORF72 form of amyotrophic lateral sclerosis and several spinocerebellar ataxias, are caused by the expansion of various microsatellite sequences in single implicated genes. The neurodegenerative and neuromuscular nature of the repeat expansion disorders considerably limits the access of researchers to appropriate cellular models of these diseases. This limitation, however, can be overcome by the application of induced pluripotent stem cell (iPSC) technology. In this paper, we review the current knowledge on the modeling of repeat expansion diseases with human iPSCs and iPSC-derived cells, focusing on the disease phenotypes recapitulated in these models. In subsequent sections, we provide basic practical knowledge regarding iPSC generation, characterization and differentiation into neurons. We also cover disease modeling in iPSCs, neuronal stem cells and specialized neuronal cultures. Furthermore, we also summarize the therapeutic potential of iPSC technology in repeat expansion diseases.

Nuclear speckles are detention centers for transcripts containing expanded CAG repeats.

The human genetic disorders caused by CAG repeat expansions in the translated sequences of various genes are called polyglutamine (polyQ) diseases because of the cellular "toxicity" of the mutant proteins. The contribution of mutant transcripts to the pathogenesis of these diseases is supported by several observations obtained from cellular models of these disorders. Here, we show that the common feature of cell lines modeling polyQ diseases is the formation of nuclear CAG RNA foci. We performed qualitative and quantitative analyses of these foci in numerous cellular models endogenously and exogenously expressing mutant transcripts by fluorescence in situ hybridization (FISH). We compared the CAG RNA foci of polyQ diseases with the CUG foci of myotonic dystrophy type 1 and found substantial differences in their number and morphology. Smaller differences within the polyQ disease group were also revealed and included a positive correlation between the foci number and the CAG repeat length. We show that expanded CAA repeats, also encoding glutamine, did not trigger RNA foci formation and foci formation is independent of the presence of mutant polyglutamine protein. Using FISH combined with immunofluorescence, we demonstrated partial co-localization of CAG repeat foci with MBNL1 alternative splicing factor, which explains the mild deregulation of MBNL1-dependent genes. We also showed that foci reside within nuclear speckles in diverse cell types: fibroblasts, lymphoblasts, iPS cells and neuronal progenitors and remain dependent on integrity of these nuclear structures.

Mouse polyQ database: a new online resource for research using mouse models of neurodegenerative diseases.

BACKGROUND: The polyglutamine (polyQ) family of disorders comprises 9 genetic diseases, including several types of ataxia and Huntington disease. Approximately two decades of investigation and the creation of more than 130 mouse models of polyQ disorders have revealed many similarities between these diseases. The disorders share common mutation types, neurological characteristics and certain aspects of pathogenesis, including morphological and physiological neuronal alterations. All of the diseases still remain incurable. DESCRIPTION: The large volume of information collected as a result of the investigation of polyQ models currently represents a great potential for searching, comparing and translating pathogenesis and therapeutic information between diseases. Therefore, we generated a public database comprising the polyQ mouse models, phenotypes and therapeutic interventions tested in vivo. The database is available at http://conyza.man.poznan.pl/ . CONCLUSION: The use of the database in the field of polyQ diseases may accelerate research on these and other neurodegenerative diseases and provide new perspectives for future investigation.

Huntington disease iPSCs show early molecular changes in intracellular signaling, the expression of oxidative stress proteins and the p53 pathway.

Huntington disease (HD) is a brain disorder characterized by the late onset of motor and cognitive symptoms, even though the neurons in the brain begin to suffer dysfunction and degeneration long before symptoms appear. There is currently no cure. Several molecular and developmental effects of HD have been identified using neural stem cells (NSCs) and differentiated cells, such as neurons and astrocytes. Still, little is known regarding the molecular pathogenesis of HD in pluripotent cells, such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). Therefore, we examined putative signaling pathways and processes involved in HD pathogenesis in pluripotent cells. We tested naïve mouse HD YAC128 iPSCs and two types of human HD iPSC that were generated from HD and juvenile-HD patients. Surprisingly, we found that a number of changes affecting cellular processes in HD were also present in undifferentiated pluripotent HD iPSCs, including the dysregulation of the MAPK and Wnt signaling pathways and the dysregulation of the expression of genes related to oxidative stress, such as Sod1. Interestingly, a common protein interactor of the huntingtin protein and the proteins in the above pathways is p53, and the expression of p53 was dysregulated in HD YAC128 iPSCs and human HD iPSCs. In summary, our findings demonstrate that multiple molecular pathways that are characteristically dysregulated in HD are already altered in undifferentiated pluripotent cells and that the pathogenesis of HD might begin during the early stages of life.

Mouse models of polyglutamine diseases in therapeutic approaches: review and data table. Part II.

Mouse models of human diseases are created both to understand the pathogenesis of the disorders and to find successful therapies for them. This work is the second part in a series of reviews of mouse models of polyglutamine (polyQ) hereditary disorders and focuses on in vivo experimental therapeutic approaches. Like part I of the polyQ mouse model review, this work is supplemented with a table that contains data from experimental studies of therapeutic approaches in polyQ mouse models. The aim of this review was to characterize the benefits and outcomes of various therapeutic strategies in mouse models. We examine whether the therapeutic strategies are specific to a single disease or are applicable to more than one polyQ disorder in mouse models. In addition, we discuss the suitability of mouse models in therapeutic approaches. Although the majority of therapeutic studies were performed in mouse models of Huntington disease, similar strategies were also used in other disease models.

Mouse models of polyglutamine diseases: review and data table. Part I.

Polyglutamine (polyQ) disorders share many similarities, such as a common mutation type in unrelated human causative genes, neurological character, and certain aspects of pathogenesis, including morphological and physiological neuronal alterations. The similarities in pathogenesis have been confirmed by findings that some experimental in vivo therapy approaches are effective in multiple models of polyQ disorders. Additionally, mouse models of polyQ diseases are often highly similar between diseases with respect to behavior and the features of the disease. The common features shared by polyQ mouse models may facilitate the investigation of polyQ disorders and may help researchers explore the mechanisms of these diseases in a broader context. To provide this context and to promote the understanding of polyQ disorders, we have collected and analyzed research data about the characterization and treatment of mouse models of polyQ diseases and organized them into two complementary Excel data tables. The data table that is presented in this review (Part I) covers the behavioral, molecular, cellular, and anatomic characteristics of polyQ mice and contains the most current knowledge about polyQ mouse models. The structure of this data table is designed in such a way that it can be filtered to allow for the immediate retrieval of the data corresponding to a single mouse model or to compare the shared and unique aspects of many polyQ models. The second data table, which is presented in another publication (Part II), covers therapeutic research in mouse models by summarizing all of the therapeutic strategies employed in the treatment of polyQ disorders, phenotypes that are used to examine the effects of the therapy, and therapeutic outcomes.