1809-P: Liver Pyruvate Carboxylase Knockout Mice Suggest Noncanonical Sources of Acetyl-CoA for Hepatic Lipid Synthesis

Abstract

Elevated hepatic de novo lipogenesis (DNL) is a key characteristic of patients with Nonalcoholic Fatty Liver Disease (NAFLD). Liver pyruvate carboxylase (PC) may be critical for DNL since PC replenishes oxaloacetate that is converted to citrate as source for acetyl-CoA during DNL. PC may also play a role in triglyceride (TG) synthesis by replenishing oxaloacetate that is used for glyceroneogenesis. Thus, PC is considered a lipogenic enzyme, though most evidence has been derived from non-liver cell culture models and indirect measures in livers of animal models. Liver-specific PC knockout mice (LPCKO) have lower circulating TG on a high fat diet, but fasting liver TG was not improved. To determine whether liver-specific PC is required for DNL and glyceroneogenesis, we examined LPCKO mice using a 1H/2H NMR approach to directly measure flux through DNL and TG-glycerol synthesis. PCf/f and LPCKO mice were exposed to either standard chow or a high sucrose diet (HSD) for 10 days. Ad libitum fed PCf/f and LPCKO mice were then administered D2O overnight. Liver lipids were extracted, and positional isotopomer analysis by 1H/2H NMR was used to determine DNL and TG-glycerol synthesis fluxes. DNL flux was not significantly different between PCf/f and LPCKO mice under standard chow conditions and only tended to be moderately lower in LPCKO mice after a short-term HSD treatment. TG-glycerol synthesis was also similar between PCf/f and LPCKO, regardless of diet. Surprisingly, liver triglyceride levels were modestly higher in standard chow fed LPCKO than PCf/f mice, and no significant differences were found between HSD-fed PCf/f and LPCKO mice. Our initial findings suggest that PC is not required for DNL and TG-glycerol synthesis during the fed state and therefore indicate that alternative pathways may exist to supply of cytosolic acetyl-CoA for lipid synthesis. Disclosure M.R. Inigo: None. S. Deja: None. B. Kucejova: None. J.A. Fletcher: None. X. Fu: None. S.C. Burgess: None. Funding Robert A. Welch Foundation (I-1804)