Elevation of hepatic de novo lipogenesis in mice with overnutrition is dependent on multiple substrates.

Abstract

Increased de novo lipogenesis (DNL) contributes to hyperlipidemia, MASLD, and ASCVD in insulin resistant subjects. However, multiple pathways support lipogenesis and few have sought to quantify the contributions of the discrete metabolic pathways that contribute to lipogenesis. In this study, antisense oligonucleotides (ASOs) targeting glucokinase (Gck), lactate dehydrogenase A (Ldha), and glutamic-pyruvic transaminase 2 (Gpt2) were utilized to restrict substrate flux from lipogenic precursors in C57BL6/J mice, comparing controls (CO) and chronic overnutrition (ON). In CO mice, ASO treatments did not significantly alter lipogenesis; however, there was a trend toward decreased hepatic triglyceride content and DNL, especially with the GPT2 ASO (TG=-46.8%; DNL=-53.7%). Expectedly, increased hepatic TG content and DNL (ON vs CO: TG=+187.9%; DNL=+41.8%) was observed in mice with chronic overnutrition. Gas chromatography-mass spectrometry analyses demonstrated increased hepatic TCA cycle metabolites (ON vs CO: fumarate +74.2%; malate +54.0%; and citrate +43.2) and decreased hepatic concentrations of multiple amino acids (ON vs CO: Leu -41.7%; Ile -45.0%; Val -56.3%; Ser -22.6%). With ON, TG content and DNL were reduced by restricting lipogenic carbon entry from alanine (GPT2: TG=-45.5%; DNL=-48.1%), lactate (LDHA: TG=-25.8%; DNL=-33.1%), or glucose (GCK: TG=-59.2%; DNL=-69.2%). Amino acids appear to be a consistent carbon source for DNL in mice; however, carbon entry from all sources is required to maintain the significantly elevated rates of hepatic DNL in chronically overfed mice. These findings may inform the development of novel therapies and underscore the importance of peripheral substrate storage and oxidation in the prevention of dyslipidemia in the metabolic syndrome.