Alternative translation initiatin as a novel strategy to block toxicity of the mutant androgen receptor in SBMA

Spinobulbar Muscular Atrophy (SBMA) is an adult onset neuromuscular disease, which only affects males and it is caused by an expansion of a triplet CAG repeat sequence present in exon 1 of the androgen receptor (AR) gene. This sequence encodes an elongated polyglutamine tract (ARpolyQ) in the N-terminus of the AR protein, which has been proved to confer toxicity to the ARpolyQ, when this is activated in response to the binding which circulating androgens, the male sex hormonal steroids. The therapeutic attempt testes so far for SBMA are based on strategies aimed to block androgen production and/or activity, as well as on AR down-regulation. The main side effect of these approaches are the appearance of relevant undesired endocrine dysfunction in male patients. In this project, we proposed a novel therapeutic approach, which is aimed to “repair” the mutant AR by removing its toxic polyQ tract, without causing an AR loss of function. To this aim we will test the possibility to enhance the synthesis of an AR isoform devoid of toxic polyQ tract, preventing the translation of the neurotoxic ARpolyQ. We will take advantage of the presence of an AUG translation start codon in the AR mRNA, which is located downstream the pathogenic CAG repeat. The use of this AUG leads to the production of an AR isoform (AR-A), which retains its androgenic activity, but lacks toxicity because is devoid of the elongated polyQ tract. We threfore subdivided the project in three aims focused: - to study AR-A and ARpolyQ levels during development and disease manifestation in SBMA mice, differentiated human SBMA iPSCs and muscle tissues of SBMA patients; - to characterize crucial androgenic properties of AR-A comparing them with ARpolyQ; - to develop an effective strategy to selectively drive AR-A translation in motoneurons and muscle cells. The shifting of translation from ARpolyQ to AR-A will be attempted via antisense oligonucleotide (ASO), phosphorodiamidate morpholino oligo (PMO), Locked nucleic acids (LNA) and a library of FDA-approved drugs and natural compounds; - to test if the positive hits are active in human SBMA iPSCs derived motoneurons or muscle cells and SBMA flies. We expect to impose AR initiation of translation at the II-AUG thus skipping the polyQ and produce nontoxic AR-A, thus decreasing the total amount of toxic ARpolyQ, without reducing the overall AR activity in target cells. This will provide a safe and tolerable potential treatment for SBMA patients.