Since the discovery of AMP-activated protein kinase (AMPK) as a central regulator of energy homeostasis, many exciting insights into its structure, regulation and physiological roles have been ...revealed. While exercise, caloric restriction, metformin and many natural products increase AMPK activity and exert a multitude of health benefits, developing direct activators of AMPK to elicit beneficial effects has been challenging. However, in recent years, direct AMPK activators have been identified and tested in preclinical models, and a small number have entered clinical trials. Despite these advances, which disease(s) represent the best indications for therapeutic AMPK activation and the long-term safety of such approaches remain to be established.
In eukaryotic cells AMP-activated protein kinase (AMPK) plays a major role in regulating cellular energy balance. AMPK responds to changes in intracellular adenine nucleotide levels, being activated ...by an increase in AMP/ADP relative to ATP. Activation of AMPK increases the rate of catabolic (ATP-generating) pathways and decreases the rate of anabolic (ATP-utilising) pathways. In addition to its role in maintaining intracellular energy balance, AMPK regulates whole body energy metabolism. Given its key role in controlling energy homeostasis, AMPK has attracted widespread interest as a potential therapeutic target for metabolic diseases, including type 2 diabetes and, more recently, cancer. Here I review the regulation of AMPK and its potential as a target for therapeutic intervention in human disease.
The recent exciting advances in our understanding of the regulation of the energy sensor AMP-activated protein kinase (AMPK), together with renewed appreciation of its importance in maintaining ...cellular function, brought together leading scientists at a recent FASEB-sponsored meeting in September 2014. Here, we report some of the highlights of this conference.
Recent research has expanded the paradigm of AMP-activated protein kinase (AMPK) as a metabolic sensor and the more global concept that AMPK has broad effects on cellular function, providing synergy between research in energy metabolism and other areas of science such as cancer, neuroscience, and inflammation. Here, Carling and Viollet summarize novel insights in the field and new avenues of future research presented at the 2014 FASEB Science Research Conference “AMPK: Biological Action and Therapeutic Perspectives,” which took place at Lucca, Italy, in September 2014.
The hydrolysis of ATP drives virtually all of the energy-requiring processes in living cells. A prerequisite of living cells is that the concentration of ATP needs to be maintained at sufficiently ...high levels to sustain essential cellular functions. In eukaryotic cells, the AMPK (AMP-activated protein kinase) cascade is one of the systems that have evolved to ensure that energy homoeostasis is maintained. AMPK is activated in response to a fall in ATP, and recent studies have suggested that ADP plays an important role in regulating AMPK. Once activated, AMPK phosphorylates a broad range of downstream targets, resulting in the overall effect of increasing ATP-producing pathways whilst decreasing ATP-utilizing pathways. Disturbances in energy homoeostasis underlie a number of disease states in humans, e.g. Type 2 diabetes, obesity and cancer. Reflecting its key role in energy metabolism, AMPK has emerged as a potential therapeutic target. In the present review we examine the recent progress aimed at understanding the regulation of AMPK and discuss some of the latest developments that have emerged in key areas of human physiology where AMPK is thought to play an important role.
Mitochondrial reactive oxygen species (ROS) production is a tightly regulated redox signal that transmits information from the organelle to the cell. Other mitochondrial signals, such as ATP, are ...sensed by enzymes, including the key metabolic sensor and regulator, AMP-activated protein kinase (AMPK). AMPK responds to the cellular ATP/AMP and ATP/ADP ratios by matching mitochondrial ATP production to demand. Previous reports proposed that AMPK activity also responds to ROS, by ROS acting on redox-sensitive cysteine residues (Cys-299/Cys-304) on the AMPK α subunit. This suggests an appealing model in which mitochondria fine-tune AMPK activity by both adenine nucleotide–dependent mechanisms and by redox signals. Here we assessed whether physiological levels of ROS directly alter AMPK activity. To this end we added exogenous hydrogen peroxide (H2O2) to cells and utilized the mitochondria-targeted redox cycler MitoParaquat to generate ROS within mitochondria without disrupting oxidative phosphorylation. Mitochondrial and cytosolic thiol oxidation was assessed by measuring peroxiredoxin dimerization and by redox-sensitive fluorescent proteins. Replacing the putative redox-active cysteine residues on AMPK α1 with alanines did not alter the response of AMPK to H2O2. In parallel with measurements of AMPK activity, we measured the cell ATP/ADP ratio. This allowed us to separate the effects on AMPK activity due to ROS production from those caused by changes in this ratio. We conclude that AMPK activity in response to redox changes is not due to direct action on AMPK itself, but is a secondary consequence of redox effects on other processes, such as mitochondrial ATP production.
AMP-activated protein kinase (AMPK) is the central component of a protein kinase cascade that plays a key role in the regulation of energy control. AMPK is activated in response to an increase in the ...ratio of AMP:ATP within the cell. Activation requires phosphorylation of threonine 172 within the catalytic subunit of AMPK by an upstream kinase. The identity of the upstream kinase in the cascade remained frustratingly elusive for many years, but was recently identified as LKB1, a kinase that is inactivated in a rare hereditary form of cancer called Peutz–Jeghers syndrome. Once activated, AMPK initiates a series of responses that are aimed at restoring the energy balance within the cell. ATP-consuming, anabolic pathways, such as fatty acid synthesis and protein synthesis are switched-off, whereas ATP-generating, catabolic pathways, such as fatty acid oxidation and glycolysis, are switched-on. More recent studies have indicated, that AMPK plays an important role in the regulation of whole body energy metabolism. The adipocyte-derived hormones, leptin and adiponectin, activate AMPK in peripheral tissues, including skeletal muscle and liver, increasing energy expenditure. In the hypothalamus, AMPK is inhibited by leptin and insulin, hormones which suppress feeding, whilst ghrelin, a hormone that increases food intake, activates AMPK. Furthermore, direct pharmacological activation of AMPK in the hypothalamus by 5-aminoimidazole-4-carboxamide ribose increases food intake in rats, demonstrating that AMPK plays a direct role in the regulation of feeding. Taken together these findings indicate that AMPK has a pivotal role in regulating pathways that control both energy expenditure and energy intake.
Herein, we demonstrate a role of AMP-activated protein kinase (AMPK) as a potent counterregulator of inflammatory signaling pathways in macrophages. Stimulation of macrophages with anti-inflammatory ...cytokines (i.e., IL-10 and TGFbeta) resulted in the rapid phosphorylation/activation of AMPK, whereas stimulation of macrophages with a proinflammatory stimulus (LPS) resulted in AMPK dephosphorylation/inactivation. Inhibition of AMPKalpha expression by RNA interference dramatically increased the mRNA levels of LPS-induced TNF-alpha, IL-6, and cyclooxygenase-2. Likewise, expression of a dominant negative AMPKalpha1 in macrophages enhanced TNF-alpha and IL-6 protein synthesis in response to LPS stimulation, while diminishing the production of IL-10. In contrast, transfection of macrophages with a constitutively active form of AMPKalpha1 resulted in decreased LPS-induced TNF-alpha and IL-6 production, and heightened production of IL-10. In addition, we found that AMPK negatively regulated LPS-induced IkappaB-alpha degradation and positively regulated Akt activation, accompanied by inhibition of glycogen synthase kinase beta and activation of CREB. Thus, AMPK directs signaling pathways in macrophages in a manner that suppresses proinflammatory responses and promotes macrophage polarization to an anti-inflammatory functional phenotype.
Increased intake of dietary carbohydrate that is fermented in the colon by the microbiota has been reported to decrease body weight, although the mechanism remains unclear. Here we use in ...vivo(11)C-acetate and PET-CT scanning to show that colonic acetate crosses the blood-brain barrier and is taken up by the brain. Intraperitoneal acetate results in appetite suppression and hypothalamic neuronal activation patterning. We also show that acetate administration is associated with activation of acetyl-CoA carboxylase and changes in the expression profiles of regulatory neuropeptides that favour appetite suppression. Furthermore, we demonstrate through (13)C high-resolution magic-angle-spinning that (13)C acetate from fermentation of (13)C-labelled carbohydrate in the colon increases hypothalamic (13)C acetate above baseline levels. Hypothalamic (13)C acetate regionally increases the (13)C labelling of the glutamate-glutamine and GABA neuroglial cycles, with hypothalamic (13)C lactate reaching higher levels than the 'remaining brain'. These observations suggest that acetate has a direct role in central appetite regulation.
Maintaining sufficient levels of ATP (the immediate source of cellular energy) is essential for the proper functioning of all living cells. As a consequence, cells require mechanisms to balance ...energy demand with supply. In eukaryotic cells the AMP-activated protein kinase (AMPK) cascade has an important role in this homeostasis. AMPK is activated by a fall in ATP (concomitant with a rise in ADP and AMP), which leads to the activation of catabolic pathways and the inhibition of anabolic pathways. Here we review the role of AMPK as an energy sensor and consider the recent finding that ADP, as well as AMP, causes activation of mammalian AMPK. We also review recent progress in structural studies on phosphorylated AMPK that provides a mechanism for the regulation of AMPK in which AMP and ADP protect it against dephosphorylation. Finally, we briefly survey some of the outstanding questions concerning the regulation of AMPK.
AMP-activated protein kinase (AMPK) plays a major role in regulating metabolism and has attracted significant attention as a therapeutic target for treating metabolic disorders. AMPK activity is ...stimulated more than 100-fold by phosphorylation of threonine 172 (Thr
). Binding of AMP to the γ subunit allosterically activates the kinase. Additionally, many small molecules, e.g. 991, have been identified that bind between the kinase domain and the carbohydrate-binding module of the β subunit, stabilising their interaction and leading to activation. It was reported recently that non-phosphorylated Thr
AMPK is activated by AMP and A769662. We present here the crystal structure of non-phosphorylated Thr
AMPK in complex with AMP and 991. This structure reveals that the activation loop, as well as the complex overall, is similar to the Thr
phosphorylated complex. We find that in the presence of AMP and 991 non-phosphorylated Thr
, AMPK is much less active than the Thr
phosphorylated enzyme. In human cells, the basal level of Thr
phosphorylation is very low (∼1%), but is increased 10-fold by treatment with 2-deoxyglucose. In cells lacking the major Thr
kinases, LKB1 and CaMKKβ, Thr
phosphorylation is almost completely abolished, and AMPK activity is virtually undetectable. Our data show that AMP and 991 binding to non-phosphorylated Thr
AMPK can induce an ordered, active-like, conformation of the activation loop explaining how AMPK activity can be measured
without Thr
phosphorylation. However, in a cellular context, phosphorylation of Thr
is critical for significant activation of AMPK.
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