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Mutant androgen receptor induces neurite loss and senescence independently of ARE binding in a neuronal model of SBMA

ABSTRACT: Spinal and bulbar muscular atrophy (SBMA) is a slowly progressing neuromuscular disease 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. AR is a ligand-activated transcription factor that regulates neuronal architecture and promotes axon regeneration; however, whether AR transcriptional functions contribute to disease pathogenesis is not fully understood. Using a differentiated PC12 cell model of SBMA, we identified dysfunction of polyQ-expanded AR in its regulation of neurite growth and maintenance. Specifically, we found that in the presence of androgens, polyQ-expanded AR inhibited neurite outgrowth, induced neurite retraction, and inhibited neurite regrowth. This dysfunction was independent of polyQ-expanded AR transcriptional activity at androgen response elements (AREs). We further showed that the formation of polyQ-expanded AR intranuclear inclusions promoted neurite retraction, which coincided with reduced expression of the neuronal differentiation marker -III-Tubulin. Finally, we revealed that cell death is not the primary outcome for cells undergoing neurite retraction; rather, these cells become senescent. Our findings reveal that mechanisms independent of AR canonical transcriptional activity underly neurite defects in a cell model of SBMA and identify senescence as a previously unappreciated pathway implicated in this pathology. These findings suggest that, in the absence of a role for AR canonical transcriptional activity in the SBMA pathologies described here, the development of SBMA therapeutics that preserve this activity may be desirable. This approach may be broadly applicable to other polyglutamine diseases such as Huntington’s disease and spinocerebellar ataxias.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE267802 | GEO | 2024/07/05

REPOSITORIES: GEO

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Project description:Emerging evidence implicates transcriptional dyseregulation within skeletal muscle in the pathogenesis of Kennedy disease/spinal bulbar muscular atrophy (KD/SBMA). We therefore broadly characterized gene expression in skeletal muscle of three independently generated mouse models of this disorder. The mouse models included a polyglutamine expanded (polyQ) AR knock-in model (AR113Q KI), a polyQ AR transgenic model (AR97Q Tg), and a transgenic mouse which overexpresses wild type AR solely in muscle (HSA-AR Tg). We performed microarray analysis of lower hindlimb muscles taken from these three models using high density oligonucleotide arrays. Changes in gene expression relative to wild type controls were evaluated separately in each strain. We validated our results using quantitative RT-PCR. Patterns of gene expression that are common to all lines and unique to each are described. When considered globally, the degree of overlap between the three models is approximately equivalent, and several patterns of gene expression relevant to the disease process were observed. Notably, patterns of gene expression typical of loss of AR function were observed in all three models, as were alterations in genes involved in cell adhesion, energy balance, Huntingtonâ??s disease, muscle atrophy and myogenesis. By comparing patterns of gene expression in three independent models of KD/SBMA, we have been able to identify candidate genes that might mediate the core myogenic features of KD/SBMA. Keywords: Gene expression in transgenic mice and disease state analysis We used microarray (38.5K oligo mouse array, which contain 35,302 of 70mer oligonucleotide probes largely derived from constitutively expressed exons and 3,482 of controls) to analyze gene expression in limb muscles of transgenic mice. Three mouse models of KD/SBMA were used: HSA-AR, AR113Q knock-in and AR97Q. HSA-AR transgenic male mice (n=5) and their WT brothers (n=8, all mice were 110-130 days of age) were used in this experiment. ARQ113-Knock In males (n=3, 3-4 months of age), and transgenic AR97Q males and WT brothers (n= 6 of each) were used in this study. For both HSA-AR and AR113Q samples, the log2 ratio of experimental samples (Cy5) and reference RNA(Cy3) was obtained, and log2 ratios from mutant samples were then subtracted from log2 ratios from WT controls. AR97Q males (Cy5) were simply compared with their WT brothers (Cy3) using a log2 ratio, rather than being first compared with reference RNA.

Project description:Together with the Estrogen, Progesterone, and Glucocorticoid Receptors, the Androgen Receptor (AR) is a member of the type I nuclear receptor superfamily, a class of transcription factors that are activated by steroid hormones1. Nuclear receptors share a common three-domain structure, comprising a highly variable amino-terminal domain (NTD), with potent transcriptional activator capability, a central two zinc finger motifs DNA-binding domain (DBD), and a well-conserved carboxy-terminal ligand-binding domain (LBD) responsible for interacting with the transcriptional machinery1. Given their modular structure, expression of isoforms resulting from alternative splicing or starting and termination events have profound effects on nuclear receptor activity and function. Several AR variants (AR-Vs) have been identified from prostate cancer clinical specimens, arising from multiple mechanisms, including genomic rearrangements2 and upregulation of splicing factors3. This seminal discovery has provided the molecular basis for a deeper understanding of AR-related diseases, with potential to be translated in identification of novel therapeutic targets and promising prognostic markers4–6. By deeply sequencing the transcriptome of human brains, here we identified AR-2 as the most expressed AR isoform. Furthermore, we found that AR-2 is widely expressed in other human tissues, forms heterodimers with the full length AR and acts as a repressor of its transcriptional activity. Delivery of this isoform via adeno-associated virus (AAV9) resulted in significant amelioration of the disease phenotype in a mouse model of spinal and bulbar muscular atrophy (SBMA), a neuromuscular disease with unmet clinical need caused by a toxic gain of function of polyglutamine-expanded (polyQ) AR7. Collectively, these results establish a physiological role of AR-2 in fine-tuning full length AR activity and demonstrate the feasibility and therapeutic benefit of modulating this variant for treating SBMA and other AR-related diseases.

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Mutant androgen receptor induces neurite loss and senescence independently of ARE binding in a neuronal model of SBMA

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