Activation of Sphingolipid Pathway in the Livers of Lipodystrophic Agpat2−/− Mice

Abstract

A several fold increase in triacylglycerol is observed in the livers of lipodystrophic Agpat2−/− mice. We have previously reported an unexpected increase in the phosphatidic acid (PA) levels in the livers of these mice and that a few specific molecular species of PA were able to transcriptionally upregulate hepatic gluconeogenesis. In the current study, we measured the metabolites and expression of associated enzymes of the sphingolipid synthesis pathway. The entire sphingolipid pathway was activated both at the gene expression and the metabolite level. The levels of some ceramides were increased by as much as ~eightfold in the livers of Agpat2−/− mice. Furthermore, several molecular species of ceramides were increased in the plasma of Agpat2−/− mice, specifically ceramide C16:0, which was threefold elevated in the plasma of both the sexes. However, the ceramides failed to increase glucose production in mouse primary hepatocytes obtained from wild-type and Agpat2−/− mice, further establishing the specificity of PA in the induction of hepatic gluconeogenesis. This study shows elevated levels of sphingolipids in the steatotic livers of Agpat2−/− mice and increased expression of associated enzymes for the sphingolipid pathway. Therefore, this study and those in the literature suggest that ceramide C16:0 could be used as a biomarker for insulin resistance/type 2 diabetes mellitus.

Sphingolipids in Obesity and Correlated Co-Morbidities: The Contribution of Gender, Age and Environment

“…However, discrepancies after HFD treatment were observed in the number of long-chain Cers in the liver, skeletal muscle, and adipose tissue (Table 1). Nevertheless, quantitative results have been contradictory: Cer C24:0 has been shown to decrease in the liver as described by Cinar and Turner [52,107] and increase as demonstrated by Bruce et al [53], as well as C24:1, that was decreased in the study from Turner [52], but increased in other similar studies [53,108,113]. C24:1 gave conflicting results also in skeletal muscle, resulting from decreased as described by Bruce in 2013 [54], but increased in another study of 2012 from Bruce [53].…”

Adipose-specific overexpression of human AGPAT2 in mice causes increased adiposity and mild hepatic dysfunction

“…A general method routinely used by us for total RNA extraction and RT-qPCR has been described. 40 Briefly, total RNA was extracted from mouse liver tissues (∼50–100 mg) using RNA STAT-60. Total RNA from adipose tissue depots was extracted using RNeasy Lipid Tissue Kit according to the manufacture’s protocol.…”

Regulated regeneration of adipose tissue in lipodystrophic Agpat2-null mice partially ameliorates hepatic steatosis

“…A general method routinely used by us for total RNA extraction and RT-qPCR has been described before. 35 , 36 Briefly, total RNA was extracted from mouse liver tissues (∼50–100 mg) using RNA STAT-60 (Tel-Test, Friendswood, TX, USA). RT-qPCR was carried out and analyzed as described below.…”