Exercise training adaptations in liver glycogen and glycerolipids require hepatic AMP-activated protein kinase in mice

Abstract

Regular exercise elicits adaptations in glucose and lipid metabolism that allow the body to meet energy demands of subsequent exercise bouts more effectively and mitigate metabolic diseases including fatty liver. Energy discharged during the acute exercise bouts that comprise exercise training may be a catalyst for liver adaptations. During acute exercise, liver glycogenolysis and gluconeogenesis are accelerated to supply glucose to working muscle. Lower liver energy state imposed by gluconeogenesis and related pathways activates AMP-activated protein kinase (AMPK), which conserves ATP partly by promoting lipid oxidation. This study tested the hypothesis that AMPK is necessary for liver glucose and lipid adaptations to training. Liver-specific AMPK12 knockout (LAKO) and wild type (WT) mice completed sedentary and exercise training protocols. Liver nutrient fluxes were quantified at rest or during acute exercise following training. Liver metabolites and molecular regulators of metabolism were assessed. Training increased liver glycogen in WT mice, but not in LAKO mice. The inability to increase glycogen led to lower glycogenolysis, glucose production, and circulating glucose during acute exercise in trained LAKO mice. Deletion of AMPK12 attenuated training-induced declines in liver diacylglycerides. In particular, training lowered the concentration of unsaturated and elongated fatty acids comprising diacylglycerides in WT mice, but not in LAKO mice. Training increased liver triacylglycerides and the desaturation and elongation of fatty acids in triacylglycerides of LAKO mice. These lipid responses were independent of differences in tricarboxylic acid cycle fluxes. In conclusion, AMPK is required for liver training adaptations that are critical to glucose and lipid metabolism. NEW & NOTEWORTHYThis study shows that the energy sensor and transducer, AMP-activated protein kinase, is necessary for an exercise training-induced: i) increase in liver glycogen that is necessary for accelerated glycogenolysis during exercise, ii) decrease in liver glycerolipids independent of TCA cycle flux, and iii) decline in the desaturation and elongation of fatty acids comprising liver diacylglycerides. The mechanisms defined in these studies have implications for use of regular exercise or AMPK-activators in patients with fatty liver.