An RNA-mediated gene therapy approach to target polyglutamine-expanded AR co-regulators and attenuate SBMA


Pre-Clinical Research

Poster Number: 276


maria pennuto, PhD, University of Padova, Ramachandran Prakasam, PhD, University of Trento, Roberta Andreotti, MS, University of Padova, Emanuela Zuccaro, PhD, University of Padova, Chris Grunseich, MD, National Institutes of Health, Udai Pandey, PhD, University of Pittsburgh Medical Center, Manuela Basso, PhD, University of Trento

Spinobulbar muscular atrophy (SBMA) is an X-linked neuromuscular disease that affects 2–5 in 100,000 people worldwide. There is no therapy to delay disease onset and progression. SBMA is caused by exonic CAG expansions coding for glutamine in the androgen receptor (AR) gene, and its dependence on androgens restricts its full manifestation to males. Binding of androgens to polyQ-expanded AR triggers SBMA through a combination of toxic gain-of-function (GOF) and loss-of-function (LOF) mechanisms that lead to motor neuron loss, muscle atrophy, mild androgen insensitivity syndrome, and metabolic syndrome. We reported that interaction of AR with its transcription co-regulators is necessary to cause disease, making this aspect of AR biology therapeutically relevant. However, inhibition of AR or its co-regulators to reduce toxic GOF may enhance its LOF. We tested an alternative approach centered on AR co-regulators that are overexpressed as a result of aberrant androgen signaling in key target tissues (e.g., skeletal muscle). Using cell lines, mice, and patient-derived specimens, we show that AR co-regulators lysine demethylase 1 (LSD1) and protein arginine methyltransferase 6 (PRMT6) are overexpressed in an androgen-dependent manner specifically in skeletal muscle of patients with SBMA and mouse models. LSD1 and PRMT6 cooperatively and synergistically transactivate AR, and their effect is enhanced by expanded polyQ. Pharmacologic and genetic silencing of LSD1 and PRMT6 attenuates polyQ-expanded AR transactivation in SBMA cells and suppresses toxicity in SBMA flies, and a preclinical approach based on miRNA-mediated silencing of LSD1 and PRMT6 attenuates disease manifestations in SBMA mice. These observations support the idea that targeting overexpressed AR co-regulators reduces AR toxic GOF without exacerbating LOF, highlighting a potential therapeutic strategy for patients with SBMA.