Alternative Translation Initiation as a novel strategy to block toxicity of the mutant Androgen Receptor in SBMA

Spinal and Bulbar Muscular Atrophy is a neurodegenerative disease linked to a CAG repeat expansion in the Androgen Receptor (AR) gene, which is translated into a polyglutamine tract (polyQ) in the AR N-terminal region. ARpolyQ acquires neurotoxic properties and aggregates after testosterone binding. Different start codons (AUGs) are involved in AR translation. I-AUG leads to translation of a full- length AR (AR-B) which includes the pathogenic polyQ tract in SBMA. II-AUG is located downstream to the CAG repeat leading to the translation of an alternative isoform named AR-A, this isoform does not contain the neurotoxic polyQ tract. Here we characterized AR-A behaviour and designed an effective strategy to selectively drive the AR translation from the II-AUG via antisense oligonucleotide (ASO) and a library of FDA approved drugs blocking ARpolyQ toxicity (GOF) without causing AR loss of function (LOF). Through analysis of AR-A expression levels, transactivation activity, aggregates formation and co- expression of AR-A and AR-polyQ we demonstrated that depletion of the AR N-terminal region in AR-A: i. did not affect AR-A translation and stability ii. maintained testosterone responsiveness, even if with a lover transactional activity compared to AR-B, but similar to ARpolyQ and iii. lead to the reduction of aggregate formation in ARpolyQ:AR-A ratio-dependent manner. Using a double report screening vector designed to detect different AR isoforms expression in relation to the signal obtained we will perform ASO and drugs screening and, furthermore, we will understand the function of AR-A homodimer and AR-A:ARpolyQ heterodimer.