Although SIRT1-deficiency did not impair the effect of metformin on reducing liver cholesterol content which is consistent with the hepatic steatosis result, the cholesterol hydroxylase CH25H, which is involved cholesterol catabolism, was upregulated in DIO mice after metformin treatment but not in Sirt1+/− mice. The gene discussed is SIRT1; the disease is Hepatic steatosis.