Cytoplasmic retention of polyglutamine-expanded androgen receptor ameliorates disease via autophagy in a mouse model of spinal and bulbar muscular atrophy.

The nucleus is the primary site of protein aggregation in many polyglutamine diseases, suggesting a central role in pathogenesis. In SBMA, the nucleus is further implicated by the critical role for disease of androgens, which promote the nuclear translocation of the mutant androgen receptor (AR). To clarify the importance of the nucleus in SBMA, we genetically manipulated the nuclear localization signal of the polyglutamine-expanded AR. Transgenic mice expressing this mutant AR displayed inefficient nuclear translocation and substantially improved motor function compared with SBMA mice. While we found that nuclear localization of polyglutamine-expanded AR is required for SBMA, we also discovered, using cell models of SBMA, that it is insufficient for both aggregation and toxicity and requires androgens for these disease features. Through our studies of cultured motor neurons, we further found that the autophagic pathway was able to degrade cytoplasmically retained expanded AR and represents an endogenous neuroprotective mechanism. Moreover, pharmacologic induction of autophagy rescued motor neurons from the toxic effects of even nuclear-residing mutant AR, suggesting a therapeutic role for autophagy in this nucleus-centric disease. Thus, our studies firmly establish that polyglutamine-expanded AR must reside within nuclei in the presence of its ligand to cause SBMA. They also highlight a mechanistic basis for the requirement for nuclear localization in SBMA neurotoxicity, namely the lack of mutant AR removal by the autophagic protein degradation pathway.

Castration restores function and neurofilament alterations of aged symptomatic males in a transgenic mouse model of spinal and bulbar muscular atrophy.

Transgenic models of neurodegenerative disease have proved uniquely powerful for delineating pathways of neuronal dysfunction and cell death. We have developed a transgenic model of the polyglutamine disease spinal and bulbar muscular atrophy (SBMA), an adult-onset, slowly progressive motor neuron disease caused by polyglutamine expansion in the androgen receptor (AR). Mice bearing a human AR with 112 glutamines reproduce many aspects of SBMA, including slowly progressive, gender-specific motor deficits, and neuronal intranuclear inclusions. Despite substantial motor deficits in male AR112Q mice, no motor neuron loss was observed, indicating that neuronal dysfunction, rather than neuronal death, is central to disease. Moreover, reduced levels of unphosphorylated neurofilament heavy chain (NF-H) were observed in motor neurons, suggesting a role for NF-H in SBMA neuronal dysfunction. The elimination of androgens by surgical castration of severely affected, aged 112Q male mice partially restored motor function as well as NF-H levels. These data suggest that hormone-based therapies designed to treat SBMA patients, even with advanced disease, are likely to be effective.