As shown in Figures 2(a) and 2(b), PDE5A-overexpressed C2C12 myotubes exhibited the elevated levels of ER stress markers such as CHOP and phosphorylated IRE-1α, as well as the increased expressions of JNK phosphorylation which is believed to be responsible for ER stress-induced insulin resistance. This evidence concerns the gene MAPK8 and Insulin resistance.