Liver Steatosis in Induced Hepatocytes From Carriers of Spinal Muscular Atrophy

Although classically characterized as a motor neuron disease, spinal muscular atrophy (SMA) is increasingly recognized as a multisystem disorder. We previously showed hepatocyte-intrinsic steatosis in SMA, raising the question of whether SMA carriers, who are typically asymptomatic, may also exhibit subclinical hepatic abnormalities.

We generated induced hepatocyte-like cells (iHeps) from induced pluripotent stem cells (iPSCs) derived from an SMA Type 2 proband, his isogenic wild-type (Iso-WT) line, and both carrier parents, comprised of three carrier lines from the father and one from the mother. Steatosis was assessed by Oil Red O staining and image analysis. Survival motor neuron (SMN) expression was evaluated by immunoblotting. Proteotranscriptomic profiling and mitochondrial respiration assays were performed. Risdiplam, an SMN2 splicing modulator, was used to assess reversibility of observed phenotypes.

SMA and carrier iHeps demonstrated increased lipid accumulation compared to Iso-WT. Risdiplam reduced steatosis by 65.9% in SMA patient-derived iHeps and by 43.6% and 56.9% in father- and mother carrier-derived iHeps, respectively. Carrier and SMA iHeps exhibited downregulation of genes involved in lipid metabolism and liver function, along with altered expression of lipid-related proteins. Mitochondrial dysfunction was present only in SMA iHeps. Carrier-derived induced motor neurons showed normal viability under oxidative stress, consistent with preserved neuromuscular function clinically.

Our data reveal hepatocyte-intrinsic lipid metabolic defects in SMA carriers, partially reversible with risdiplam. These findings suggest subclinical hepatic involvement in carriers and support further investigation into the systemic impact of SMN deficiency.