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 Statement
Marc-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.
Footnotes
Financial support: RK was supported by Cure SMA/Families of SMA Canada; Muscular Dystrophy Association (USA) (grant number 575466); Canadian Institutes of Health Research (CIHR) (grant number PJT-156379); and the E-Rare-2 program from the CIHR (grant number ERL-138414). MEH was funded by CIHR (grant number FDN 143278). THG was supported by UK SMA Research Consortium and SMA Europe. SHP was supported by Tenovus (Scotland) and The Euan Macdonald Centre for Research into Motor Neurone Diseases. TMW was supported by BBSRC ISP. BLS was supported by ERANET E-Rare FaSMALS (grant number 3ER30_160673). MLH was supported by the Darwin Trust. The Vanderbilt Mouse Metabolic Phenotyping Center was supported by NIH grant DK59637. The University of Massachusetts Medical School National Mouse Metabolic Phenotyping Center (MMPC) is supported by NIH grant (5U2C-DK093000). LC is supported by a Vanier CIHR Scholarship. MOD was supported by Frederick Banting and Charles Best CIHR Doctoral Research Award.
Conflict of interest statement: Marc-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.
Synopsis The Smn2B/- mice, a model of spinal muscular atrophy, represent a good model of microvesicular steatohepatitis. They offer a reliable, low-cost early onset model to identify molecular players in the pathogenesis of NAFLD in both the adult and pediatric population.
List of abbreviations
- AGC
- automatic gain control
- ALP
- alkaline phosphatase
- ALT
- alanine aminotransferase
- AST
- aspartate aminotransferase
- Bax
- BCL2 associated X protein
- DAVID
- The Database for Annotation, Visualization and Integrated Discovery
- ES
- Enrichment Score
- FasR
- Fas receptor
- H&E
- Hematoxylin & eosin
- HFD
- high fat diet
- IGF-1
- insulin-like growth factor 1
- IGFbp1
- insulin like growth factor binding protein 1
- IGF1R
- insulin like growth factor 1 receptor
- igfals
- insulin like growth factor binding protein acid labile subunit
- IPA
- ingenuity pathway analysis
- MCD
- methionine and choline deficient diet
- MCL
- Markov Clustering Algorithm
- NAFLD
- non-alcoholic fatty liver disease
- NASH
- non-alcoholic steatohepatitis
- NEFA
- non-esterified fatty acid
- P
- postnatal day
- p21
- cyclin dependent kinase inhibitor 1A
- p53
- tumor protein p53
- PAS
- Periodic acid-Schiff
- SMA
- spinal muscular atrophy
- SMN1
- Survival motor neuron 1
- TMT
- Tandem Mass Tagging
- TNFR1
- TNF receptor superfamily member 1A