Abstract
Spinal muscular atrophy (SMA) is a neuromuscular disease caused by loss of the SMN1 gene. Although lower motor neurons are a primary target, there is evidence that peripheral organ defects contribute to SMA. Current SMA gene therapy uses a single, high titre intravenous bolus of AAV9-SMN resulting in impressive, yet limited amelioration of the clinical phenotype. However, risks of this treatment include liver toxicity. Intrathecal administration is under clinical trial but was interrupted due to safety concerns in a concomitant animal study. As there is no direct comparison between the different delivery strategies while avoiding high dose toxicity, we injected SMA mice with low dose scAAV9-cba-SMN either intravenously (IV) for peripheral SMN restoration or intracerebroventricularly (ICV) for CNS-focused SMN restoration. Here, IV injections restored SMN in peripheral tissues but not CNS, while ICV injections mildly increased SMN in the periphery and the CNS. Consequently, only ICV treatment rescued motor neuron degeneration. Surprisingly, both treatments resulted in an impressive rescue of survival, weight, motor function, and peripheral phenotypes including liver and pancreas pathology. Our work highlights independent contributions of peripheral organs to SMA pathology and suggests that treatments should not be restricted to the motor neuron.
Competing Interest Statement
RK received honoraria and travel accommodations from Roche as an invited speaker at their global and national board meetings in 2019. RK and the Ottawa Hospital Research Institute have a licensing agreement with Biogen for the Smn2B/- mouse model. MOD received honoraria and travel accommodations from Biogen for speaking engagements at the SMA Summit 2018 held in Montreal, Canada and SMA Academy 2019 held in Toronto, Canada. These COI are outside the scope of this study. All other authors have no competing interests to declare.
