A mouse model for spinal muscular atrophy provides insights into non-alcoholic fatty liver disease pathogenesis

Abstract

Background & aims Spinal muscular atrophy (SMA) is an inherited neuromuscular disorder leading to paralysis and death in children. SMA patients are more susceptible to dyslipidemia as well as liver steatosis, features reproduced in SMA mouse models. As current pre-clinical models of NAFLD are invariably imperfect and generally take a long time to develop, the rapid development of liver steatosis in SMA mice provides a means to identify molecular markers of non-alcoholic fatty liver disease (NAFLD). Here, we investigated whether Smn2B/- mice, a model of severe SMA, display typical features of NAFLD/non-alcoholic steatohepatitis (NASH).Methods Biochemical, histological, electron microscopy, proteomic, and high-resolution respirometry were used.Results The Smn2B/- mice develop steatohepatitis early in life. The consequent liver damage arises from mitochondrial reactive oxygen species production and results in impaired hepatic function including alterations in protein output, complement, coagulation, iron homeostasis, and IGF-1 metabolism. The steatohepatitis is reversible by AAV9-SMN gene therapy. The NAFLD phenotype is likely due to non-esterified fatty acid (NEFA) overload from peripheral lipolysis, subsequent to hyperglucagonemia compounded by reduced muscle use. Mitochondrial β-oxidation contributed to hepatic damage as we observed enhanced hepatic mitochondrial β-oxidation and reactive oxygen species production. Hepatic mitochondrial content, however, was decreased. In contrast to typical NAFLD/NASH, the Smn2B/- mice lose weight due to their neurological condition, develop hypoglycemia and do not develop hepatic fibrosis.Conclusion The Smn2B/- mice represent a good model of microvesicular steatohepatitis. Like other models, it is not representative of the complete NAFLD/NASH spectrum. Nevertheless, it offers a reliable, low-cost, early onset model that is not dependent on diet to identify molecular players in NAFLD pathogenesis and can serve as one of the very few models of microvesicular steatohepatitis for both adult and pediatric populations.Competing Interest StatementMarc-Olivier Deguise 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. Rashmi Kothary 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. Thomas H. Gillingwater has served on global and UK advisory boards for Roche. These COI are outside the scope of this study. All other authors have no competing interests to declare.List of abbreviationsAGCautomatic gain controlALPalkaline phosphataseALTalanine aminotransferaseASTaspartate aminotransferaseBaxBCL2 associated X proteinDAVIDThe Database for Annotation, Visualization and Integrated DiscoveryESEnrichment ScoreFasRFas receptorH&EHematoxylin & eosinHFDhigh fat dietIGF-1insulin-like growth factor 1IGFbp1insulin like growth factor binding protein 1IGF1Rinsulin like growth factor 1 receptorigfalsinsulin like growth factor binding protein acid labile subunitIPAingenuity pathway analysisMCDmethionine and choline deficient dietMCLMarkov Clustering AlgorithmNAFLDnon-alcoholic fatty liver diseaseNASHnon-alcoholic steatohepatitisNEFAnon-esterified fatty acidPpostnatal dayp21cyclin dependent kinase inhibitor 1Ap53tumor protein p53PASPeriodic acid-SchiffSMAspinal muscular atrophySMN1Survival motor neuron 1TMTTandem Mass TaggingTNFR1TNF receptor superfamily member 1AView Full Text