Liver SMN restoration rescues the Smn2B/- mouse model of spinal muscular atrophy.

Background: The liver is a key metabolic organ, acting as a hub to metabolically connect various tissues. Spinal muscular atrophy (SMA) is a neuromuscular disorder whereby patients have an increased susceptibility to developing dyslipidaemia and liver steatosis. It remains unknown whether fatty liver is due to an intrinsic or extrinsic impact of survival motor neuron (SMN) protein depletion.

Methods: Using an adeno-associated viral vector with a liver specific promoter (albumin), we restored SMN protein levels in the liver alone in Smn^2B/- mice, a model of SMA. Experiments assessed central and peripheral impacts using immunoblot, immunohistochemistry, and electron microscopy techniques.

Findings: We demonstrate that AAV9-albumin-SMN successfully expresses SMN protein in the liver with no detectable expression in the spinal cord or muscle in Smn^2B/- mice. Liver intrinsic rescue of SMN protein was sufficient to increase survival of Smn^2B/- mice. Fatty liver was ameliorated while key markers of liver function were also restored to normal levels. Certain peripheral pathologies were rescued including muscle size and pancreatic cell imbalance. Only a partial CNS recovery was seen using a liver therapeutic strategy alone.

Interpretation: The fatty liver phenotype is a direct impact of liver intrinsic SMN protein loss. Correction of SMN protein levels in liver is enough to restore some aspects of disease in SMA. We conclude that the liver is an important contributor to whole-body pathology in Smn^2B/- mice.

Funding: This work was funded by Muscular Dystrophy Association (USA) [grant number 963652 to R.K.]; the Canadian Institutes of Health Research [grant number PJT-186300 to R.K.].