Identifying the Mechanism Behind the Role of the AR N/C Interaction in SBMA
Abstract
Spinal bulbar muscular atrophy (SBMA) is an X-linked, progressive neuromuscular degenerative disease affecting approximately 1 in 50000 males worldwide. Patients display progressively worsening muscle weakness, leading to difficulty ambulating and with chewing and swallowing, predisposing patients to dangerous secondary indications such as aspiration pneumonia. There is currently no cure or effective treatment for SBMA. SBMA is caused by a CAG repeat expansion in the androgen receptor gene which is translated to an expanded polyglutamine tract in the androgen protein. This mutation causes AR to misfold and aggregate, leading to toxicity and eventual death of lower motor neurons and muscle. While significant headway has been made in researching the molecular mechanisms behind SBMA, there is much that we still do not understand about the process by which an expanded polyglutamine tract leads to toxicity in the affected cell types. One of these gaps in our knowledge is the mechanism by which an interdomain interaction between the amino and carboxyl termini of AR, termed the N/C interaction, provides protection in SBMA. Previous research has shown that blocking this interaction is protective in cell and mouse models of SBMA, but the details as to how remain elusive. This study sought to shed light on this mechanism by investigating several aspects of AR biology that were likely to be affected by alterations in the N/C interaction. We first hypothesized that polyglutamine expanded androgen receptor would demonstrate an increased N/C interaction compared to wild-type. We found the opposite to be true, leading to a new hypothesis that perhaps different forms of the N/C interaction, that occurring intra- or inter- molecularly, might play different roles in SBMA pathology. As such, we investigated one of these forms through investigation of the role of dimerization in SBMA. Additionally, we sought to determine whether the N/C interaction altered the AR interactome and, if so, whether information from this altered interactome might describe certain pathways or key proteins that drive the protection offered by blocking the N/C interaction. Finally, we sought to investigate the potential of selective androgen receptor modulators as potential therapeutics for SBMA.In this study, we found that AR homodimerization- investigated in part through a novel biochemical analysis of AR dimerization- plays an important role in SBMA pathogenesis. Blocking AR dimerization reduces AR aggregation in cell models, as well as increases cytoplasmic AR localization and AR degradation compared to dimerization-competent AR. Additionally, we find that blocking the N/C interaction dramatically alters the AR interactome. Further blocking phosphorylation at serine 16, a post-translational modification that has been shown to be increased when the N/C interaction is blocked, further alters the AR interactome. These altered interactomes share a few features, notably that they both contain proteasomal components as well as mitochondrial specific proteins, suggesting important roles for both protein turnover and mitochondrial association might play a role in the protective mechanism provided by blocking the N/C interaction. Finally, we found that, though some of the SARMs investigated were able to significantly block the N/C interaction, all SARMs tested induced AR aggregation in the absence of hormone treatment, suggesting that the state of the N/C interaction and protection from AR aggregation are not as closely correlated as previously thought. Overall, the studies described here present significant insight into the mechanism of the N/C interaction’s role in SBMA- including a novel role for AR homodimerization in SBMA pathogenesis, an investigation into the changes in the AR interactome caused by altering the N/C interaction and phosphorylation at the nearby serine 16, and screening of compounds from a unique class of molecules known as selective androgen receptor modulators- as well as AR biology as a whole.
Subject Area
Biochemistry|Neurosciences|Cellular biology|Genetics
Recommended Citation
Lisberg, Allison, "Identifying the Mechanism Behind the Role of the AR N/C Interaction in SBMA" (2024). ProQuest ETD Collection - Thomas Jefferson University. AAI31144523.
https://jdc.jefferson.edu/dissertations/AAI31144523
