Novel protective modifiers in mouse models of spinal muscular atrophy

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Spinal Muscular Atrophy (SMA) is a neuromuscular disease caused by the homozygous deletion or mutation in the survival motor neuron-1 (SMN1) gene resulting in extremely low levels of the SMN protein. Without treatment, the majority of SMA cases progress rapidly and lead to mortality by age 2. SMA is uniquely positioned for therapy, however, as a nearly identical gene called SMN2 can be modulated to express the functional SMN protein. A recently approved, highly efficacious therapy called Spinraza adopts this strategy and has brought promise to the SMA patient community. Despite this breakthrough, it is widely hypothesized that a long-term strategy will require a combinatorial approach to address the complexity of this disease, and additional therapeutic strategies need to be established. Towards this aim, the past decade of research has led to the elucidation of key molecular events that contribute to the pathology of SMA as well as several factors that modulate disease severity. Referred to as protective modifiers, these factors represent potential targets for combinatorial therapy. In this work we establish a strategy to identify and characterize novel protective modifiers in mouse models of SMA. Our approach utilizes adenoassociated virus serotype 9 (AAV9) to express putative modifiers in mouse models, effectively allowing us to determine their effects in vivo. Using our experimental system, we confirm that a previously controversial modifier, Plastin-3, reduces severity in mouse models of SMA. We also identify miR-23a, DOK7, and [alpha]-synuclein as novel protective modifiers of SMA. These insights implicate microRNA dysregulation, neuromuscular junction organization, and synaptic transmission as disease modifying pathways that contain potential therapeutic candidates for the treatment of SMA.