Hepatic ketogenesis supports liver lipid homeostasis during acute exercise but is not required for exercise training to mitigate liver steatosis in mice

The acceleration of hepatic lipid disposal during acute exercise has been proposed as a contributor to the anti-steatotic effects of exercise training. Ketogenesis, which produces acetoacetate (AcAc) and β-hydroxybutyrate (βOHB) from fatty acids, is among the lipid disposal pathways stimulated by exercise. This study tested the hypothesis that hepatic ketogenesis is necessary for exercise training to lower liver lipids. Liver-specific 3-hydroxymethylglutaryl-CoA synthase 2 knockout (HMGCS2 KO) mice and wild type (WT) littermates underwent sedentary, acute exercise, and exercise training protocols. Liver ketone bodies and lipids were determined via mass spectrometry platforms. Stable isotope infusions in conscious, unrestrained mice defined mitochondrial oxidative fluxes at rest and during exercise. Loss of hepatic HMGCS2 decreased liver AcAc and βOHB concentrations and impaired their increase during exercise. Liver triacylglycerides (TAGs) were comparable between genotypes at rest (i.e., ad libitum fed and short fasted conditions). In contrast, liver TAGs were elevated in HMGCS2 KO mice following acute, non-exhaustive exercise. Liver TCA cycle flux was higher in KO mice at rest. During exercise, TCA cycle flux increased in both WT and KO mice but was not different between genotypes with greater exercise duration. This suggests that enhanced disposal of lipids via the TCA cycle may prevent liver lipid accumulation in HMGCS2 KO mice under sedentary conditions, but not during exercise. Unexpectedly, exercise training decreased liver TAGs similarly in both HMGCS2 KO and WT mice. In conclusion, hepatic ketogenesis supports liver lipid homeostasis during acute exercise, but is not required for exercise training to lower liver lipids.