The obesity epidemic has led to an increased incidence of non–alcoholic fatty liver disease (NAFLD) and type 2 diabetes. AMP–activated protein kinase (Ampk) regulates energy homeostasis and is activated by cellular stress, hormones and the widely prescribed anti–type 2 diabetic drug metformin1,2. Ampk phosphorylates murine acetyl–CoA carboxylase3,4 (Acc) 1 at Ser79 and Acc2 at Ser212, inhibiting the conversion of acetyl–CoA to malonyl–CoA, a precursor in fatty acid synthesis5 as well as an allosteric inhibitor of fatty acid transport into mitochondria for oxidation6. To test the physiological impact of these phosphorylation events we generated mice with alanine knock–in mutations in both Acc1 (Ser79) and Acc2 (Ser212) (Acc double knock–in, AccDKI). These mice have elevated lipogenesis and lower fatty acid oxidation compared to wild–type (WT) mice, which contribute to the progression of insulin resistance, glucose intolerance and NAFLD, but not obesity. Remarkably, AccDKI mice made obese by high–fat feeding, are refractory to the lipid–lowering and insulin–sensitizing effects of metformin. These findings establish that inhibitory phosphorylation of Acc by Ampk is essential for the control of lipid metabolism, and in the setting of obesity, for metformin–induced improvements in insulin action.

Mitochondrial uncoupling protein 1 (UCP1) is enriched within interscapular brown adipose tissue (iBAT) and beige (also known as brite) adipose tissue 1,2 , but its thermogenic potential is reduced with obesity and type 2 diabetes 3-5 for reasons that are not understood. Serotonin (5-hydroxytryptamine, 5-HT) is a highly conserved biogenic amine that resides in non-neuronal and neuronal tissues that are specifically regulated via tryptophan hydroxylase 1 (Tph1) and Tph2, respectively 6-8 . Recent findings suggest that increased peripheral serotonin 9 and polymorphisms in TPH1 are associated with obesity 10 ; however, whether this is directly related to reduced BAT Reprints and permissions information is available online at

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Nonalcoholic fatty liver disease (NAFLD) is a growing worldwide epidemic and an important risk factor for the development of insulin resistance, type 2 diabetes, nonalcoholic steatohepatitis (NASH), and hepatic cellular carcinoma (HCC). Despite the prevalence of NAFLD, lifestyle interventions involving exercise and weight loss are the only accepted treatments for this disease. Over the last decade, numerous experimental compounds have been shown to improve NAFLD in preclinical animal models, and many of these therapeutics have been shown to increase the activity of the cellular energy sensor AMP-activated protein kinase (AMPK). Because AMPK activity is reduced by inflammation, obesity, and diabetes, increasing AMPK activity has been viewed as a viable therapeutic strategy to improve NAFLD. In this review, we propose three primary mechanisms by which AMPK activation may improve NAFLD. In addition, we examine the mechanisms by which AMPK is activated. Finally, we identify 27 studies that have used AMPK activators to reduce NAFLD. Future considerations for studies examining the relationship between AMPK and NAFLD are highlighted.

Canagliflozin, dapagliflozin and empagliflozin, all recently approved for treatment of Type 2 diabetes, were derived from the natural product phlorizin. They reduce hyperglycemia by inhibiting glucose reuptake by SGLT2 in the kidney, without affecting intestinal glucose uptake by SGLT1. We now report that canagliflozin also activates AMP-activated protein kinase (AMPK), an effect also seen with phloretin (the aglycone breakdown product of phlorizin), but not to any significant extent with dapagliflozin, empagliflozin or phlorizin. AMPK activation occurred at canagliflozin concentrations measured in human plasma in clinical trials, and was caused by inhibition of Complex I of the respiratory chain, leading to increases in cellular AMP or ADP. Although canagliflozin also inhibited cellular glucose uptake independently of SGLT2, this did not account for AMPK activation. Canagliflozin also inhibited lipid synthesis, an effect that was absent in AMPK knockout cells and that required phosphorylation of ACC1 and/or ACC2 at the AMPK sites. Oral administration of canagliflozin activated AMPK in mouse liver, although not in muscle, adipose tissue or spleen. As phosphorylation of acetyl-CoA carboxylase by AMPK is known to lower liver lipid content, these data suggest a potential additional benefit of canagliflozin therapy compared to other SGLT2 inhibitors.

Despite widespread use of statins to reduce low-density lipoprotein cholesterol (LDL-C) and associated atherosclerotic cardiovascular risk, many patients do not achieve sufficient LDL-C lowering due to muscle-related side effects, indicating novel treatment strategies are required. Bempedoic acid (ETC-1002) is a small molecule intended to lower LDL-C in hypercholesterolemic patients, and has been previously shown to modulate both ATP-citrate lyase (ACL) and AMP-activated protein kinase (AMPK) activity in rodents. However, its mechanism for LDL-C lowering, efficacy in models of atherosclerosis and relevance in humans are unknown. Here we show that ETC-1002 is a prodrug that requires activation by very long-chain acyl-CoA synthetase-1 (ACSVL1) to modulate both targets, and that inhibition of ACL leads to LDL receptor upregulation, decreased LDL-C and attenuation of atherosclerosis, independently of AMPK. Furthermore, we demonstrate that the absence of ACSVL1 in skeletal muscle provides a mechanistic basis for ETC-1002 to potentially avoid the myotoxicity associated with statin therapy.

Summary The incidence of hepatocellular carcinoma (HCC) is rapidly increasing due to the prevalence of obesity and non-alcoholic fatty liver disease, but the molecular triggers that initiate disease development are not fully understood. We demonstrate that mice with targeted loss of function point mutations within the AMP-activated protein kinase (AMPK) phosphorylation sites acetyl-CoA carboxylase 1 (ACC1 Ser79Ala) and ACC2 (ACC2 Ser212Ala) have increased liver de novo lipogenesis (DNL) and liver lesions. The same mutation in ACC1 also increases DNL and proliferation human liver cancer cells. Consistent with these findings, a novel, liver specific ACC inhibitor (ND-654), that mimics the effects of ACC phosphorylation, inhibits hepatic DNL and the development of HCC, improving survival of tumor-bearing rats when used alone and in combination with the multi-kinase inhibitor sorafenib. These studies highlight the importance of DNL and dysregulation of AMPK-mediated ACC phosphorylation in accelerating HCC and the potential of ACC inhibitors for treatment.

Metformin is the most commonly prescribed medication for type 2 diabetes, owing to its glucose-lowering effects, which are mediated through the suppression of hepatic glucose production (reviewed in refs. 1-3). However, in addition to its effects on the liver, metformin reduces appetite and in preclinical models exerts beneficial effects on ageing and a number of diverse diseases (for example, cognitive disorders, cancer, cardiovascular disease) through mechanisms that are not fully understood 1-3. Given the high concentration of metformin in the liver and its many beneficial effects beyond glycemic control, we reasoned that metformin may increase the secretion of a hepatocyte-derived endocrine factor that communicates with the central nervous system 4. Here we show, using unbiased transcriptomics of mouse hepatocytes and analysis of proteins in human serum, that metformin induces expression and secretion of growth differentiating factor 15 (GDF15). In primary mouse hepatocytes, metformin stimulates the secretion of GDF15 by increasing the expression of activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP; also known as DDIT3). In wild-type mice fed a high-fat diet, oral administration of metformin increases serum GDF15 and reduces food intake, body mass, fasting insulin and glucose intolerance; these effects are eliminated in GDF15 null mice. An increase in serum GDF15 is also associated with weight loss in patients with type 2 diabetes who take metformin. Although further studies will be required to determine the tissue source(s) of GDF15 produced in response to metformin in vivo, our data indicate that the therapeutic benefits of metformin on appetite, body mass and serum insulin depend on GDF15. Metformin is one of the most widely used medications in the world. It is a strong base that exists in its protonated form at physiological pH and therefore does not pass through cellular membranes easily. In rodents, oral administration of metformin (250-300 mg kg-1 body weight) results in clinically relevant plasma concentrations of approximately 10-15 μM; however, concentrations in the