Fig. 7.
Summary of the microbiota-induced changes in energy and lipid metabolism identified in our study. Energy metabolites are increased in the serum and are reflected by an upregulation of related genes in the liver transcriptome. Triglyceride (TG) levels are decreased in the serum and increased in adipose tissue and the liver of CONV-R mice after a 4 h fast. The serum reduction in TG is caused by a decrease in chylomicrons (CM). Lipid absorption is not reduced in CONV-R mice, and we propose that lipid clearance is increased. In agreement, we have previously shown that a microbiota increases suppression of angiopoietin-like protein 4/fasting-induced adipose factor (Angptl4/Fiaf) (16), an inhibitor of LPL, which will promote increased lipid clearance. VLDL production in the liver is increased in CONV-R mice, which may explain why VLDL-TG serum levels are not reduced in CONV-R mice despite increased clearance. Furthermore, phosphatidylcholine (16:0/18:1), which has been identified as a potent endogenous PPARα ligand, is increased in the serum and liver of CONV-R mice. Increased activation of PPARα may promote increased lipid clearance by inducing expression of LPL.