Molecular Insights into Neuromuscular Decline in Spinal and Bulbar Muscular Atrophy


Pre-Clinical Research

Poster Number: S116


Anastasia Gromova, PhD, UC Irvine, Byeong Cha, UC Irvine, Nhat Nguyen, UC Irvine, Diya Garg, UC Irvine, Albert La Spada, MD/PhD, UC Irvine

Spinal and Bulbar Muscular Atrophy (SBMA, also known clinically as Kennedy’s Disease), is a rare, X-linked neuromuscular disorder caused by a CAG (encoding glutamine, Q) repeat expansion in the first exon of the Androgen Receptor gene (polyQ-AR). Once considered purely a lower motor neuron disease, building evidence supports a causal and primary role of polyQ-AR expression in skeletal muscle in driving neuromuscular decline in patients and animal models. Through multiple Cre-lox models, we show that excision of polyQ-AR from skeletal muscle is sufficient to fully rescue neuromuscular deficits in SBMA model mice. Increased lifespan of muscle-rescued mice allows for the investigation of unexplored yet highly patient-relevant secondary phenotypes such as cardiomyopathy and hepatic steatosis for the first time. On the contrary, excision of polyQ-AR from motor neurons using two different motor neuron Cre drivers failed to rescue any neuromuscular disease and seems to exacerbate the disease course in one of the drivers. However, there remains much to understand about how polyQ-AR causes myopathy later in life despite, at younger ages, correctly facilitating male development. By deeply profiling skeletal muscle of pre-symptomatic animals at the molecular level, we identify the early and robust repression of the sarcomere gene program. Simultaneously, pre-symptomatic SBMA muscle shows mobilization of protein synthesis and turnover pathways, increased calcium flux, and pro-hypertrophic signaling as potentially compensatory mechanisms to maintain muscle function in early disease stages. PolyQ-AR-driven down-regulation of critical muscle genes involves the nuclear egress of MEF2 but remains to be fully elucidated. Understanding how polyQ-AR interfaces with and perturbs the physiological control of gene expression in muscle is critical to developing effective therapies for this debilitating condition.