Multi-technique comparison of atherogenic and MCD NASH models highlights changes in sphingolipid metabolism

Abstract

Lipotoxicity is a key player in the pathogenesis of nonalcoholic steatohepatitis (NASH), a progressive subtype of nonalcoholic fatty liver disease (NAFLD). In the present study, we combine histological, transcriptional and lipidomic approaches to dissociate common and specific alterations induced by two classical dietary NASH models (atherogenic (ATH) and methionine/choline deficient (MCD) diet) in C57BL/6J male mice. Despite a similar degree of steatosis, MCD-fed mice showed more pronounced liver damage and a worsened pro-inflammatory and pro-fibrogenic environment than ATH-fed mice. Regarding lipid metabolism, the ATH diet triggered hepatic counter regulatory mechanisms, while the MCD diet worsened liver lipid accumulation by a concomitant increase in lipid import and reduction in lipid export. Liver lipidomics revealed sphingolipid enrichment in both NASH models that was accompanied by an upregulation of the ceramide biosynthesis pathway and a significant rise in dihydroceramide levels. In contrast, the phospholipid composition was not substantially altered by the ATH diet, whereas the livers of MCD-fed mice presented a reduced phosphatidylcholine to phosphatidylethanolamine (PC/PE) ratio and a strong depletion in phospholipids containing the sum of 34–36 carbons in their fatty acid chains. Therefore, the assessment of liver damage at the histological and transcriptional level combined with a lipidomic analysis reveals sphingolipids as shared mediators in liver lipotoxicity and pathogenesis of NASH.

NAFLD Preclinical Models: More than a Handful, Less of a Concern?

“…Moreover, MCD increased hepatic damage, lobular inflammation, lipogranulomas, tissue fibrosis, and liver enzymes compared to mice fed a cholesterol/cholate-rich diet. In addition, transcriptional analyses revealed a dysregulation in extracellular matrix remodeling and hepatic stellate cell activation in response to MCD, but not an atherogenic diet [41]. Altogether, these data pointed towards a more severe form of NASH in MCD mice [41], which was in line with previous studies showing that MCD triggered extensive hepatic inflammation in rats [43] and mice [44][45][46] within a very short time frame.…”

“…In addition, transcriptional analyses revealed a dysregulation in extracellular matrix remodeling and hepatic stellate cell activation in response to MCD, but not an atherogenic diet [41]. Altogether, these data pointed towards a more severe form of NASH in MCD mice [41], which was in line with previous studies showing that MCD triggered extensive hepatic inflammation in rats [43] and mice [44][45][46] within a very short time frame. To overcome the lack of severe hepatic fibrosis often observed in preclinical models, mice are commonly fed MCD [47] or a diet low in/deficient for choline (CD) [48].…”

“…In line with others [24,42], wild-type C57BL/6 mice fed a cholesterol/cholate-rich diet showed increases in hepatic cholesterol and free fatty acids, while MCD mice predominantly accumulated triglycerides in their livers [41]. Strikingly, MCD caused a reduction in liver weights, whereas atherogenic diet did not [41]. Moreover, MCD increased hepatic damage, lobular inflammation, lipogranulomas, tissue fibrosis, and liver enzymes compared to mice fed a cholesterol/cholate-rich diet.…”

“…Other dietary variants were explored by Montandon et al [41], comparing the high-fat atherogenic diet (60% fat plus 1.25% cholesterol and 0.5% cholic acid) versus the commonly used methionine/choline-deficient diet (MCD). In line with others [24,42], wild-type C57BL/6 mice fed a cholesterol/cholate-rich diet showed increases in hepatic cholesterol and free fatty acids, while MCD mice predominantly accumulated triglycerides in their livers [41]. Strikingly, MCD caused a reduction in liver weights, whereas atherogenic diet did not [41].…”

Too Much of a Good Thing? An Evolutionary Theory to Explain the Role of Ceramides in NAFLD

“…Ceramides have also been observed as a signature of the NASH disease state in disparate mouse models of the condition, including those that are not obese. For example, an unbiased comparison of two diet-mediated mouse NASH models, the methionine choline deficient and the atherogenic diets, identified alterations in sphingolipid metabolism as a common feature in both ( 34 ). This study included a thorough exploration of histological, transcriptional, and lipidomic changes in both models.…”