Authors: Robert N Helsley, Se-Hyung Park, Hemendra J Vekaria, Patrick G Sullivan, Lindsey R Conroy, Ramon C Sun, María Del Mar Romero, Laura Herrero, Joanna Bons, Christina D King, Jacob Rose, Jesse G Meyer, Birgit Schilling, C Ronald Kahn, Samir Softic
Originally published: www.sciencedirect.com on Feb. 21, 2023
Abstract
Background & Aims
The consumption of sugar and high-fat diet (HFD) promotes the development of obesity and metabolic dysfunction. Despite their well-known synergy, the mechanisms by which sugar worsens the outcomes associated with a HFD intake is largely elusive.
Methods
Six week-old, male, C57 B l/6 J mice were fed either chow or HFD provided with regular, fructose- or glucose-sweetened water. Moreover, cultured AML12 hepatocytes were engineered to overexpress ketohexokinase C (KHK–C) using lentivirus or to knockdown CPT1α using CRISPR-Cas9. The cell culture experiments were complimented with in-vivo studies using mice with hepatic overexpression of KHK–C and in mice with liver-specific CPT1α knockout. We used comprehensive metabolomics, electron microscopy, mitochondrial substrate phenotyping, proteomics and acetylome analysis to investigate the underlying mechanism.
Results
Fructose supplementation of mice on normal chow, and fructose or glucose supplementation of mice on HFD increase KHK–C, an enzyme that catalyzes the first step of fructolysis. Elevated KHK–C is associated with an increase in lipogenic proteins, such as ACLY, without affecting their mRNA expression. An increase in KHK–C also correlates with acetylation of CPT1α at K508, and lower CPT1α protein in vivo. In vitro, KHK–C overexpression lowers CPT1α and increases triglyceride accumulation. The effects of KHK–C are, in part, replicated by a knockdown of CPT1α. An increase in KHK–C correlates negatively with CPT1α protein in mice fed sugar and HFD, but also in genetically obese db/db and lipodystrophic FIRKO mice. Mechanistically, overexpression of KHK–C in vitro increases global protein acetylation and decreases the major cytoplasmic deacetylase, SIRT2.
Conclusions
KHK–C-induced acetylation is a novel mechanism by which dietary fructose augments lipogenesis and decreases fatty acid oxidation to support the development of metabolic complications.
Impact and Implications
Fructose is a highly lipogenic nutrient whose negative consequences have been largely attributed to increased de novo lipogenesis. Here we show that fructose upregulates ketohexokinase, which in turn modifies global protein acetylation, including acetylation of CPT1a, to decrease fatty acid oxidation. Our findings broaden the impact of dietary sugar beyond its lipogenic role and have implications on drug development aimed at reducing the harmful effects attributed to sugar metabolism.