Antisense RNA sequences modulating the ataxin-1 message: molecular model of gene therapy for spinocerebellar ataxia type 1, a dominant-acting unstable trinucleotide repeat disease

Neuromodulation of the cerebellum rescues movement in a mouse model of ataxia

Deep brain stimulation (DBS) relieves motor dysfunction in Parkinson's disease, and other movement disorders. Here, we demonstrate the potential benefits of DBS in a model of ataxia by targeting the cerebellum, a major motor center in the brain. We use the Car8 mouse model of hereditary ataxia to test the potential of using cerebellar nuclei DBS plus physical activity to restore movement. While low-frequency cerebellar DBS alone improves Car8 mobility and muscle function, adding skilled exercise to the treatment regimen additionally rescues limb coordination and stepping. Importantly, the gains persist in the absence of further stimulation. Because DBS promotes the most dramatic improvements in mice with early-stage ataxia, we postulated that cerebellar circuit function affects stimulation efficacy. Indeed, genetically eliminating Purkinje cell neurotransmission blocked the ability of DBS to reduce ataxia. These findings may be valuable in devising future DBS strategies.

Targeted Oligonucleotides for Treating Neurodegenerative Tandem Repeat Diseases

Nucleotide repeat disorders encompass more than 30 diseases, most of which show dominant inheritance, such as Huntington's disease, spinocerebellar ataxias, and myotonic dystrophies. Yet others, including Friedreich's ataxia, are recessively inherited. A common feature is the presence of a DNA tandem repeat in the disease-associated gene and the propensity of the repeats to expand in germ and in somatic cells, with ensuing neurological and frequently also neuromuscular defects. Repeat expansion is the most frequent event in these diseases; however, sequence contractions, deletions, and mutations have also been reported. Nucleotide repeat sequences are predisposed to adopt non-B-DNA conformations, such as hairpins, cruciform, and intramolecular triple-helix structures (triplexes), also known as H-DNA. For gain-of-function disorders, oligonucleotides can be used to target either transcripts or duplex DNA and in diseases with recessive inheritance oligonucleotides may be used to alter repressive DNA or RNA conformations. Most current treatment strategies are aimed at altering transcript levels, but therapies directed against DNA are also emerging, and novel strategies targeting DNA, instead of RNA, are described. Different mechanisms using modified oligonucleotides are discussed along with the structural aspects of repeat sequences, which can influence binding modes and efficiencies.

Allele-specific silencing of mutant Ataxin-7 in SCA7 patient-derived fibroblasts

Polyglutamine (polyQ) disorders are inherited neurodegenerative conditions defined by a common pathogenic CAG repeat expansion leading to a toxic gain-of-function of the mutant protein. Consequences of this toxicity include activation of heat-shock proteins (HSPs), impairment of the ubiquitin-proteasome pathway and transcriptional dysregulation. Several studies in animal models have shown that reducing levels of toxic protein using small RNAs would be an ideal therapeutic approach for such disorders, including spinocerebellar ataxia-7 (SCA7). However, testing such RNA interference (RNAi) effectors in genetically appropriate patient cell lines with a disease-relevant phenotype has yet to be explored. Here, we have used primary adult dermal fibroblasts from SCA7 patients and controls to assess the endogenous allele-specific silencing of ataxin-7 by two distinct siRNAs. We further identified altered expression of two disease-relevant transcripts in SCA7 patient cells: a twofold increase in levels of the HSP DNAJA1 and a twofold decrease in levels of the de-ubiquitinating enzyme, UCHL1. After siRNA treatment, the expression of both genes was restored towards normal levels. To our knowledge, this is the first time that allele-specific silencing of mutant ataxin-7, targeting a common SNP, has been demonstrated in patient cells. These findings highlight the advantage of an allele-specific RNAi-based therapeutic approach, and indicate the value of primary patient-derived cells as useful models for mechanistic studies and for measuring efficacy of RNAi effectors on a patient-to-patient basis in the polyQ diseases.

Microprecision delivery of oligonucleotides in a 3D tissue model and its characterization using optical imaging

Despite significant potential of oligonucleotides (ONs) for therapeutic and diagnostic applications, rapid and widespread intracellular delivery of ONs in cells situated in tissues such as skin, head and neck cavity, and eye has not been achieved. This study was aimed at evaluating the synergistic combination of microneedle (MN) arrays and biochemical approaches for localized intratissue delivery of oligonucleotides in living cells in 3D tissue models. This synergistic combination was based on the ability of MNs to precisely deliver ONs into tissues to achieve widespread distribution, and the ability of biochemical agents (streptolysin O (SLO) and cholesterol conjugation to ONs) to enhance intracellular ON delivery. The results of this study demonstrate that ON probes were uniformly coated on microneedle arrays and were efficiently released from the microneedle surface upon insertion in tissue phantoms. Co-insertion of microneedles coated with ONs and SLO into 3D tissue models resulted in delivery of ONs into both the cytoplasm and nucleus of cells. Within a short incubation time (35 min), ONs were observed both laterally and along the depth of a 3D tissue up to a distance of 500 μm from the microneedle insertion point. Similar widespread intratissue distribution of ONs was achieved upon delivery of ON-cholesterol conjugates. Uniformity of ON delivery in tissues improved with longer incubation times (24 h) postinsertion. Using cholesterol-conjugated ONs, delivery of ON probes was limited to the cytoplasm of cells within a tissue. Finally, delivery of cholesterol-conjugated anti-GFP ON resulted in reduction of GFP expression in HeLa cells. In summary, the results of this study provide a novel approach for efficient intracellular delivery of ONs in tissues.

Targeting RNA splicing for disease therapy

Splicing of pre-messenger RNA into mature messenger RNA is an essential step for the expression of most genes in higher eukaryotes. Defects in this process typically affect cellular function and can have pathological consequences. Many human genetic diseases are caused by mutations that cause splicing defects. Furthermore, a number of diseases are associated with splicing defects that are not attributed to overt mutations. Targeting splicing directly to correct disease-associated aberrant splicing is a logical approach to therapy. Splicing is a favorable intervention point for disease therapeutics, because it is an early step in gene expression and does not alter the genome. Significant advances have been made in the development of approaches to manipulate splicing for therapy. Splicing can be manipulated with a number of tools including antisense oligonucleotides, modified small nuclear RNAs (snRNAs), trans-splicing, and small molecule compounds, all of which have been used to increase specific alternatively spliced isoforms or to correct aberrant gene expression resulting from gene mutations that alter splicing. Here we describe clinically relevant splicing defects in disease states, the current tools used to target and alter splicing, specific mutations and diseases that are being targeted using splice-modulating approaches, and emerging therapeutics.

Mesenchymal stem cell transplantation ameliorates motor function deterioration of spinocerebellar ataxia by rescuing cerebellar Purkinje cells

Background

Spinocerebellar ataxia (SCA) refers to a disease entity in which polyglutamine aggregates are over-produced in Purkinje cells (PCs) of the cerebellum as well as other neurons in the central nervous system, and the formation of intracellular polyglutamine aggregates result in the loss of neurons as well as deterioration of motor functions. So far there is no effective neuroprotective treatment for this debilitating disease although numerous efforts have been made. Mesenchymal stem cells (MSCs) possess multi-lineage differentiation potentials as well as immuno-modulatory properties, and are theoretically good candidates for SCA treatment. The purpose of this study is to investigate whether transplantation of human MSCs (hMSCs) can rescue cerebellar PCs and ameliorate motor function deterioration in SCA in a pre-clinical animal model.

Method

Transgenic mice bearing poly-glutamine mutation in ataxin-2 gene (C57BL/6J SCA2 transgenic mice) were serially transplanted with hMSCs intravenously or intracranially before and after the onset of motor function loss. Motor function of mice was evaluated by an accelerating protocol of rotarod test every 8 weeks. Immunohistochemical stain of whole brain sections was adopted to demonstrate the neuroprotective effect of hMSC transplantation on cerebellar PCs and engraftment of hMSCs into mice brain.

Results

Intravenous transplantation of hMSCs effectively improved rotarod performance of SCA2 transgenic mice and delayed the onset of motor function deterioration; while intracranial transplantation failed to achieve such neuroprotective effect. Immunohistochemistry revealed that intravenous transplantation was more effective in the preservation of the survival of cerebellar PCs and engraftment of hMSCs than intracranial injection, which was compatible to rotarod performance of transplanted mice.

Conclusion

Intravenous transplantation of hMSCs can indeed delay the onset as well as improve the motor function of SCA2 transgenic mice. The results of this preclinical study strongly support further exploration of the feasibility to transplant hMSCs for SCA patients.

The neuroscientist's melting pot: immunology, cell transplantation and other delivery systems, and enlightenment of disease etiology and treatment

A snapshot of the current state of play with respect to a number of neurological disease causes and their potential treatments from a cell transplantation perspective, was provided at the 14th annual meeting of American Society for Neural Therapy and Repair (ASNTR). Parkinson's disease and related studies were heavily featured, with Alzheimer's disease, aging and spinal cord injury also proving to be well represented. A number of studies looked at different delivery systems including stem cells or adeno-associated virus vectors, both as proof-of-principles and also their potential as treatments, delivering neurotrophic factors. 'Simple' ways to help battle these disorders, such as dietary modification or supplementation were also revealed. Transplantation was explored both in vivo and in cell culture, where ways to improve cell survival or cause differentiation were investigated. A few reports also shed light on the likelihood of an immune response following transplantation, an important consideration for any potential treatment.