TPH1 and fatty liver disease: In order to investigate the functional role of GDS in hepatic steatosis in vivo, we generated gut-specific Tph1 knockout (KO) (Villin-Cre+/–; Tph1flox/flox, herein named Tph1 GKO) mice (Supplementary Fig. 1d, e) and induced hepatic steatosis with 8 weeks of HFD feeding.