Neurodegenerative disorders associated with protein aggregation include nine untreatable diseases caused by CAG/glutamine tract (polyQ) expansions. One of these disorders, spinobulbar muscular atrophy (SBMA), is characterized by degeneration of lower motor neurons and is caused by a mutation in the androgen receptor (AR) gene. The mutant protein undergoes hormone-dependent nuclear translocation, unfolding and oligomerization, steps that are critical to toxicity and to the development of progressive proximal limb and bulbar muscle weakness in men. Although the disease causing mutation was identified two decades ago, treatments available to SBMA patients remain largely supportive. Furthermore, the cellular pathways that degrade the mutant protein remain incompletely defined, and this lack of knowledge hinders the development of disease-modifying therapies. The objective of this application is to define the role of the Hsp90-based chaperone machinery in the protein quality control decisions that govern polyQ AR degradation. Our central hypothesis is that Hsp70 and Hsp90 have essentially opposing roles in the triage of the polyQ AR, in that Hsp70 promotes substrate ubiquitination whereas Hsp90 inhibits ubiquitination. This hypothesis springs from our preliminary data showing that association with Hsp90 stabilizes the polyQ AR, while unfolding of the mutant protein leads to ubiquitination by Hsp70-dependent E3 ligases. Here we will use genetic and pharmacological tools to define the consequences of allosterically activating Hsp70-dependent ubiquitination. Additionally, as our data point to contributions from both skeletal muscle and motor neurons to the disease phenotype, we will use genetic approaches to determine the extent to which toxicity at each site must be targeted to achieve beneficial therapeutic effects. The rationale of the proposed work is that establishing the mechanisms that regulate polyQ AR degradation will identify targets that can be exploited by the development of new therapies. Genetic and biochemical approaches will be used to determine the extent to which allosteric activators of Hsp70 promote clearance of the polyQ AR (Aim 1), to identify critical sties of polyQ AR toxicity in SBMA mice (Aim 2), and to establish the effects of novel, small molecule allosteric activators of Hsp70 in SBMA mice (Aim 3). These studies are expected to have a significant positive impact by defining pathways that limit SBMA toxicity while providing proof-of-concept data supporting a new therapeutic approach. As Hsp70 also regulates quality control decisions governing the turnover of other mutant proteins that cause neurodegeneration, we expect that the approaches defined here will inform therapeutic strategies that will be broadly applicable.

Public Health Relevance

of the proposed studies to public health is that they will define allosteric activation of Hsp70 as a strategy to promote degradation of the polyQ AR, the mutant protein that causes SBMA. This work will characterize both genetic and pharmacological Hsp70 activators, with the expectation that they will ameliorate the SBMA phenotype in model systems and speed the advance toward disease-modifying therapies.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Cell Death and Injury in Neurodegeneration Study Section (CDIN)
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Gubitz, Amelie
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University of Michigan Ann Arbor
Schools of Medicine
Ann Arbor
United States
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Nath, Samir R; Yu, Zhigang; Gipson, Theresa A et al. (2018) Androgen receptor polyglutamine expansion drives age-dependent quality control defects and muscle dysfunction. J Clin Invest 128:3630-3641
Milioto, Carmelo; Malena, Adriana; Maino, Eleonora et al. (2017) Beta-agonist stimulation ameliorates the phenotype of spinal and bulbar muscular atrophy mice and patient-derived myotubes. Sci Rep 7:41046
Nath, Samir R; Lieberman, Andrew P (2017) The Ubiquitination, Disaggregation and Proteasomal Degradation Machineries in Polyglutamine Disease. Front Mol Neurosci 10:78
Giorgetti, Elisa; Yu, Zhigang; Chua, Jason P et al. (2016) Rescue of Metabolic Alterations in AR113Q Skeletal Muscle by Peripheral Androgen Receptor Gene Silencing. Cell Rep 17:125-136
Rocchi, Anna; Milioto, Carmelo; Parodi, Sara et al. (2016) Glycolytic-to-oxidative fiber-type switch and mTOR signaling activation are early-onset features of SBMA muscle modified by high-fat diet. Acta Neuropathol 132:127-44
Polanco, Maria Josè; Parodi, Sara; Piol, Diana et al. (2016) Adenylyl cyclase activating polypeptide reduces phosphorylation and toxicity of the polyglutamine-expanded androgen receptor in spinobulbar muscular atrophy. Sci Transl Med 8:370ra181
Giorgetti, Elisa; Lieberman, Andrew P (2016) Polyglutamine androgen receptor-mediated neuromuscular disease. Cell Mol Life Sci 73:3991-9
Rusmini, Paola; Polanco, Maria Josefa; Cristofani, Riccardo et al. (2015) Aberrant Autophagic Response in The Muscle of A Knock-in Mouse Model of Spinal and Bulbar Muscular Atrophy. Sci Rep 5:15174
Pratt, William B; Gestwicki, Jason E; Osawa, Yoichi et al. (2015) Targeting Hsp90/Hsp70-based protein quality control for treatment of adult onset neurodegenerative diseases. Annu Rev Pharmacol Toxicol 55:353-71
Chua, Jason P; Reddy, Satya L; Yu, Zhigang et al. (2015) Disrupting SUMOylation enhances transcriptional function and ameliorates polyglutamine androgen receptor-mediated disease. J Clin Invest 125:831-45

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