ATF3 and obesity due to melanocortin 4 receptor deficiency: Further support for our hypothesis was obtained from the results of cell experiments, the expression of the Gdf15 mRNA and ISR-related genes Ddit3 and Atf3 was increased in the epididymal WAT and BAT, but not the liver, indicating an important role for the ISR-GDF15 axis, at least from the pharmacological perspective, and potentially represents a therapeutic target for type 2 diabetes and obesity (Figure 6E).