Mtrr hypomorphic mutation alters liver morphology, metabolism and fuel storage in mice

Nonalcoholic fatty liver disease (NAFLD) is associated with dietary folate deficiency and mutations in genes required for one‑carbon metabolism. However, the mechanism through which this occurs is unclear. To improve our understanding of this link, we investigated liver morphology, metabolism and fuel storage in adult mice with a hypomorphic mutation in the gene methionine synthase reductase (Mtrr(gt)). MTRR enzyme is a key regulator of the methionine and folate cycles. The Mtrr(gt) mutation in mice was previously shown to disrupt one‑carbon metabolism and cause a wide-spectrum of developmental phenotypes and late adult-onset macrocytic anaemia. Here, we showed that livers of Mtrr(gt/gt) female mice were enlarged compared to control C57Bl/6J livers. Histological analysis of these livers revealed eosinophilic hepatocytes with decreased glycogen content, which was associated with down-regulation of genes involved in glycogen synthesis (e.g., Ugp2 and Gsk3a genes). While female Mtrr(gt/gt) livers showed evidence of reduced β-oxidation of fatty acids, there were no other associated changes in the lipidome in female or male Mtrr(gt/gt) livers compared with controls. Defects in glycogen storage and lipid metabolism often associate with disruption of mitochondrial electron transfer system activity. However, defects in mitochondrial function were not detected in Mtrr(gt/gt) livers as determined by high-resolution respirometry analysis. Overall, we demonstrated that adult Mtrr(gt/gt) female mice showed abnormal liver morphology that differed from the NAFLD phenotype and that was accompanied by subtle changes in their hepatic metabolism and fuel storage.