Investigating the Molecular Mechanisms of Neurite Loss in Spinal and Bulbar Muscular Atrophy
Abstract
Spinal and bulbar muscular atrophy (SBMA) is a slowly progressing, X-linked neuromuscular disease characterized by progressive bulbar and proximal limb muscle weakness, fasciculations, dysarthria, dysphagia, and mild androgen insensitivity. SBMA is caused by a polyglutamine (polyQ)-encoding CAG repeat expansion in the androgen receptor (AR) gene, leading to AR aggregation, lower motor neuron death, and muscle atrophy in the presence of androgens. AR is a ligand-activated transcription factor that provides trophic support in the CNS and PNS, promotes axon regeneration, and regulates neuronal architecture. Prior studies in SBMA cell models revealed that polyQ-expanded AR induces neurite loss; however the mechanisms underlying this pathology and the contribution of AR transcriptional functions are not fully understood.In this work, we investigated the molecular mechanisms of neurite loss in SBMA and the requirement of AR transcriptional activity in this pathology using PC12 cells, which differentiate to extend neurites upon nerve growth factor (NGF) treatment. Previously published PC12 cell differentiation protocols failed to consider the variability in differentiation rates between different PC12 cell clonal variants. Thus, we established a PC12 cell differentiation protocol to quantify neurite densities over time through live-cell imaging, and determined a standardized neurite density at which cells are sufficiently differentiated for downstream analyses. We employed this protocol to investigate the role of polyQ-expanded AR transcriptional activity in neurite growth and maintenance in SBMA. We found that hormone-bound polyQ-expanded AR inhibits neurite outgrowth, induces neurite loss by enhancing neurite retraction, and inhibits neurite regrowth upon neurite retraction, independent of its transcriptional activity at androgen response elements (AREs). We further revealed that polyQ-expanded AR intranuclear inclusion formation promotes neurite retraction, which occurs alongside reduced β-III-Tubulin expression and the induction of senescence. Overall, our findings reveal senescence as a previously unappreciated pathway in SBMA pathology and demonstrate that polyQ-expanded AR transcription at AREs does not contribute to neurite loss in SBMA. These findings suggest that inhibiting AR transcriptional functions at AREs may not be required for an effective therapeutic for SBMA patients.
Subject Area
Neurosciences|Biochemistry|Biology
Recommended Citation
Karliner, Jordyn, "Investigating the Molecular Mechanisms of Neurite Loss in Spinal and Bulbar Muscular Atrophy" (2024). ProQuest ETD Collection - Thomas Jefferson University. AAI31236852.
https://jdc.jefferson.edu/dissertations/AAI31236852
