University of Utah
The mission of our laboratory is the development of therapeutics for inherited diseases of the nervous system with an emphasis on spinocerebellar ataxias, amyotrophic lateral sclerosis (ALS), and Parkinsonīs disease.
First, a look back through time at the history of SCA2
Our work on SCA2 represents an effort funded more than two decades by the NINDS. It began when Dr. Pulst and a colleague Dr. Sid Starkman visited a large SCA2 family in Syracuse NY in the early 1990’s. Later with other groups the SCA2 gene was mapped to Chr. 12, and Drs. Pulst and Starkman demonstrated anticipation in the original family suggesting that the causative gene mutation was likely a repeat expansion (Pulst et al., 1993). The gene discovery was published shortly thereafter (Pulst et al., 1996). The discovery demonstrated that ATXN2 had an expanded CAG repeat encoding a polyglutamine, and that ATXN2 is a highly evolutionarily conserved gene. At the time, the only hint on the function of ATXN2 was that it had RNA binding domains. Subsequent work to characterize ATXN2 followed two directions of investigation, discovery of ATXN2 interacting proteins, and the production and characterization of SCA2 mouse models. Chronologically there was much overlap in these efforts.
ATXN2 interacting proteins
Initial efforts to discover ATXN2 interacting proteins was by employing use of the yeast two-hybrid (Y2H) system, a method adopted by Dr. Scoles in the lab between ’95-‘96 to identify interactors to the NF2 protein (Scoles et al., 1998; Scoles et al., 2000; Scoles et al., 2006). By using Y2H we discovered the RNA binding protein ATXN2 binding protein 1 (A2BP1 / RBFOX1) as an ATXN2 interactor further supporting ATXN2 having a role in regulation of RNAs (Shibata et al., 2000). Later work done collaboratively with Ilya Bezprozvanny demonstrated that ATXN2 interacts with the inotisol triphosphate receptor protein (ITPR1) linking ATXN2 to a role in regulating calcium internal storage (Liu et al., 2009). Our studies on ATXN2 regulation of calcium movement is in collaboration with Tom Otis and Meera Pratap (UCLA) with focus primarily on hyperexcitability of SCA2 neurons (Meera et al., 2016). In SCA2, calcium is highly regluated by a feedback circuit involving mGlur1 (Meera et al., 2017).
SCA2 mouse models
We have two primary SCA2 mouse models in the lab, including ATXN2-Q127 and BAC-Q72. The ATXN2-Q127 mouse has the human ATXN2 cDNA driven by a promoter for specific expression in Purkinje cells (Pcp2) while the BAC-Q72 mouse has the human ATXN2 gene with all its introns and exons driven by 16kb of human upstream sequence. Both of these models have very similar age-dependent SCA2 phenotypes, including progressively reduced rotarod performance, progressive reduction of expression of specific Purkinje cell genes that we initially discovered by transcriptome analyses, and progressive reduction of Purkinje cell intrinsic firing frequency (Hanson et al., 2013; Dansithong et al., 2015).
SCA2 antisense oligonucleotide therapy
Toward developing a therapy for SCA2 we produced antisense oligonucleotides (ASOs) targeting ATXN2, and tested in a proof of concept study their efficacy for restoring the SCA2 phenotypes of our ATXN2-Q127 and BAC-Q72 mouse models. Our approach employs an ASO targeting the mutant and normal copy of the ATXN2 gene mRNA which we believe would be well-tolerated because mice null for the Atxn2 gene have no neurodegeneration (Kiehl et al., 2006). We treated SCA2 mice at approximately the time of phenotype onset at 8 weeks of age by intracerebroventricular (ICV) injection, and evaluated mice on the rotarod at specific timepoints thereafter out to 21 weeks of age. We observed that the ASO treated mice had a significantly better rotarod performance than control mice. At the study endpoints we evaluated the cerebellar proteins finding for ASO treated animals that the expressions of 6 key proteins were restored to levels as in wild-type. We also observed that the intrinsic Purkinje cell firing frequencies were restored by ASO treatment. The effect of the ATXN2 ASO for improving SCA2 phenotypes was seen in both SCA2 mouse models (Scoles et al., 2017). This proof of concept study supports our ongoing efforts to refine our ASO approach for targeting ATXN2 as a therapy for SCA2.
ALS in SCA2
Some SCA2 patients look like ALS patients but with added ataxia. This prompted Aaron Gitler to investigate CAG repeat structures in ATXN2 in ALS patients, revealing that some ALS patients have intermediate CAG length expansions (Elden et al., 2010). Thereafter we published a meta-analysis that showed that ALS risk is significantly associated with ATXN2 repeat length, where intermediate repeat lengths of 27-28 were associated with low risk, but for 32-33 repeats ALS risk reached a maximum (Neuenschwander et al., 2014). We then partnered with Dr. Gitler to show that survival of TDP43 ALS mice was improved when normal Atxn2 gene expression was reduced by crossing the TDP43 mouse with our Atxn2 knockout mouse. The study also showed that the same result could be achieved using an ASO targeting expression of the mouse Atxn2 gene, and that the underlying pathology was reduction of TDP43 positive stress granules with reduced Atxn2 expression (Becker et al., 2017).
Staufen 1 and stress granules in neurodegenerative disease
We have found that stress granule production is stimulated when ATXN2 is polyglutamine expanded. By studying SCA2 mouse cerebellar transcriptomes we have also discovered SCA2-related mRNAs that localize to SCA stress granules where their fates are determined. One example includes the sequestration of the PCP2 mRNA to stress granules in SCA2 patient derived fibroblasts where the message decays, accounting for the reduced Pcp2 expression that we observed in SCA2 mouse cerebella. mRNA fates appear to be regulated by substantial elevations in the ATXN2 interacting protein staufen 1 (STAU1) that colocalizes with ATXN2 in stress granules and SCA2 patient Purkinje cell inclusion bodies, associated with abnormal accumulations of autophagosomes. Genetic reduction of STAU1 expression improves the motor phenotype of SCA2 mice, also improving the expression of SCA2-related genes in the cerebellum (Paul et al., 2018). Because we have also observed increased STAU1 levels in cells of a TDP-43 mouse model, STAU1 may represent a therapeutic target for SCA2 as well as ALS.
News featuring our findings on Staufen 1
Quantitative high throughput compound screening (qHTS)
Past funding to Dr. Scoles and Dr. Pulst included screening for compounds lowering ATXN2 expression toward developing small molecule therapeutics for SCA2. This work was performed as a cooperative agreement with National Institutes of Health (NCATS). We with Dr. Duong Huynh presently have another qHTS effort with NCATS to identify small molecule therapeutics lowering alpha synuclein expression for Parkinson’s disease, funded by the Michael J. Fox Foundation. The alpha synuclein study follows up on another MJFF funded study for creation of the cell line screening assay (Dansithong et al., 2015). Studies are ongoing.
Deep brain stimulation for treating cerebellar ataxia
This study tests the hypothesis that deep brain stimulation could successfully treat the symptoms of degenerative cerebellar ataxias. Deep brain stimulation is frequently used to treat neurological conditions such as Parkinson’s disease, essential tremor, and numerous other neurological conditions. Using rats that have progressive Purkinje cell loss and exhibit tremors and lack of gait coordination, we are surgically implanting electrodes to repeatedly stimulate targets within the brain. The therapy affects the activity of different targets within the brain in a way that partially restores healthy communication between neurons. The dentate nucleus is the preferred target because it is one of the most important cerebellar regions controlling motor activity. We are also implanting recording electrodes to investigate neuronal signaling controlling motor coordination symptoms. This project represents the opportunity to not only prove the concept of a major treatment opportunity for degenerative cerebellar ataxias, but also to greatly enrich our understanding of the neurological changes that directly lead to associated motor symptoms. This study is led by Collin Anderson with funding by the National Ataxia Foundation.
Selected past grants:
RC4NS073009 Drug discovery for spinocerebellar ataxia type 2.
R01NS33123 Spinocerebellar ataxia type 2 gene and gene product.
R56NS33123 Spinocerebellar ataxia type 2 gene and gene product.
R21NS081182 Antisense oligonucleotides for treating spinocerebellar ataxia type 2.
R37NS033123 Spinocerebellar ataxia type 2 gene and gene product.
R01NS097903 RNA granules in cerebellar neurodegeneration.
U01NS103883 Antisense oligonucleotides for treating spinocerebellar ataxia type 2.
R21NS103009 Characterization of ATXN2 as a target for ALS in SCA2 motor neurons.
R21NS104799 Deep cerebellar stimulation to treat degenerative cerebellar ataxias.
Michael J. Fox Foundation Compounds lowering alpha-synuclein expression.
Harrington Discovery Institute Compounds lowering Staufen 1 expression.
National Ataxia Foundation Deep brain stimulation for cerebellar ataxia.
Last updated: September 11, 2018