To evaluate STAT3 and miR21 implication in liver steatosis also in vivo, we treated 5 weeks aged C57/BL6 mice for 72 weeks with metformin, an established anti-diabetic drug, that is able to modulate STAT3 signaling by repressing IL-6-dependent phosphorylation of STAT320,21. The gene discussed is STAT3; the disease is fatty liver disease.