ATF4 and fatty liver disease: Consistent with a previous study 6, HFD induced hepatic steatosis in Atf4+/+ mice, but not in Atf4−/− mice, as demonstrated by oil red O and haematoxylin and eosin staining (Fig. 2D) and significant hepatic and serum TG accumulation in Atf4+/+ mice (Fig. 2E and F).