To assess the metabolic effects of chronic activation of AMP-activated protein kinase (AMPK) in liver, we generated a new transgenic (Tg) mouse model expressing constitutively active (CA)-AMPK-alpha1 in liver. In the short-term activation, the TgCA-AMPK-alpha 1 mice exhibited minimal phenotype, but the Tg liver had elevated sterol regulatory element-binding protein (SREBP)-2 mRNA level and a parallel increase in transcripts of its target genes. UCP2 mRNA level was elevated. In the long-term activation, the TgCA-AMPK-alpha 1 mice had markedly reduced white fat mass. The Tg liver had reduced mRNA expression of SREBP-1c and its target genes. Remarkably, the Tg mice were resistant to a high-fat diet-induced obesity. These data suggest that short-term chronic activation of AMPK-alpha 1 in liver leads to compensatory increase in lipogenic gene expression due to increased SREBP-2 expression, and long-term chronic activation of AMPK-alpha 1 decreases expression of SREBP-1c and its target genes, which results in reduced fat storage. (C) 2008 Elsevier Inc. All rights reserved.