ATF4 and fatty liver disease: Thirdly, it is proposed that the exercise-induced hepatic steatosis improvement in obese mice with GCN2 deficiency was mediated by other upstream eIF2α kinases, eIF2α/ATF4 signaling, and AMP-activated protein kinase (AMPK)/deacetylase sirtuin-1 (SIRT1)/peroxisome proliferator-activated receptor (PPAR) alpha pathway in the liver.