AMPK与代谢综合征

能量代谢失衡是肥胖和代谢综合征的主要原因。在调节细胞能量状态的蛋白激酶级联反应中,AMP激活的蛋白激酶(AMPK)是其中枢组成部分。AMPK的活性受AMP/ATP比值的调节。应激反应可通过ATP的产生减少或利用增加,使细胞内AMP/ATP的比值增加,从而激活AMPK。激活的AMPK可激发一系列的反应来恢复细胞内的能量平衡。AMPK可启动分解代谢途径,如脂肪酸氧化和糖酵解,从而增加ATP的产生,同时关闭合成代谢途径,如脂肪酸合成和蛋白合成,减少ATP的消耗。AMPK不仅可以在细胞水平作为能量的感受器,还可以通过激素和细胞因子,如瘦素、脂联素和ghrelin来参与调节机体的能量消耗和能量摄入。新近的研究发现二甲双胍类抗糖尿病药物可以激活AMPK,调节糖代谢,提示AMPK有可能在预防机体发生代谢性疾病,如代谢综合征、肥胖和2型糖尿病中起作用。因而,阐明AMPK在不同组织及整体水平上对能量贮存与消耗的调节是今后该领域的研究热点,并且AMPK的级联反应有可能成为治疗肥胖和代谢综合征的有效靶标。     

AMPK integrates nutrient and hormonal signals to regulate food intake and energy balance through effects in the hypothalamus and peripheral tissues

The evolutionarily conserved serine/threonine kinase, AMP-activated protein kinase (AMPK), functions as a cellular fuel gauge that regulates metabolic pathways in glucose and fatty acid metabolism and protein synthesis. Recent data strongly implicate the AMPK–acetyl CoA carboxylase (ACC)–malonyl CoA pathway in the hypothalamus in the regulation of food intake, body weight and hepatic glucose production. Furthermore, data indicate that AMPK is a mediator of the effects of adipocyte-derived and gut-derived hormones and peptides on fatty acid oxidation and glucose uptake in peripheral tissues. Studies are now elucidating the potential role of kinases upstream of AMPK in these metabolic effects. In addition, recently, several novel downstream effectors of AMPK have been identified. The AMPK pathway in the hypothalamus and peripheral tissues coordinately integrates inputs from multiple hormones, peptides and nutrients to maintain energy homeostasis.     

抵抗素在肝脏胰岛素抵抗中的作用及其机制

目的： 探讨抵抗素在肝脏胰岛素抵抗中的作用及其可能的机制。方法： 将载有抵抗素基因的重组腺病毒经尾静脉注射构建高抵抗素血症小鼠模型,同时设正常对照组及病毒对照组,取肝脏组织切片行PAS糖原染色半定量观察肝糖代谢的变化;以Western blotting检测肝腺苷酸活化蛋白激酶（AMPK）的磷酸化,以磷酸化AMPK/总AMPK的比值代表AMPK激活程度;以实时 PCR检测肝组织糖异生关键酶葡萄糖6磷酸酶（G6Pase）和磷酸烯醇式丙酮酸羧激酶（PEPCK）mRNA表达水平的变化。结果： 重组腺病毒注射第5 d,获得血中抵抗素高表达构建了高抵抗素血症动物模型,糖原染色示高抵抗素血症小鼠肝糖原含量较正常对照及病毒对照组降低,分别为0.78±0.06 vs 0.93±0.13、0.89±0.05（P<0.05）;高抵抗素血症组肝AMPK磷酸化水平较正常对照及病毒对照组下降, 磷酸化AMPK/总AMPK比值分别为0.78±0.06 vs 0.93±0.13、 0.89±0.05（P<0.05）。高抵抗素血症小鼠G6Pase和PEPCK 的mRNA表达升高,高抵抗素血症组、对照组及空载病毒组G6Pase分别为2.136±0.857 vs 1.353±0.490、 1.250±0.770 （P<0.05）;高抵抗素血症组、对照组及空载病毒组 PEPCK分别为3.54±0.90 vs 2.75±0.78、 2.63±0.67（P<0.05）。结论： 抵抗素可能通过抑制肝脏AMPK活性,增加肝糖异生关键酶的表达而影响机体肝糖代谢,降低肝糖储量,参与肝脏胰岛素抵抗的形成。     

Metabolomics of the effect of AMPK activation by AICAR on human umbilical vein endothelial cells

AMP-activated protein kinase (AMPK) is a metabolic master switch expressed in a great number of cells and tissues. AMPK is thought to modulate the cellular response to different stresses that increase cellular AMP concentration. The adenosine analog, 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) is an AMPK activator used in many studies to assess the effects of AMPK activation on cellular metabolism and function. However, the effect of AICAR on cell metabolism reaches many different pathways and metabolites, some of which do not seem to be fully related to AMPK activation. We have now for the first time used NMR metabolomics on human umbilical vein endothelial cells (HUVEC) for the study of the global metabolic impact of AMPK activation by AICAR. In our study, incubation with AICAR activates AMPK and is associated with, among others, broad metabolic alterations in energy metabolism and phospholipid biosynthesis. Using NMR spectroscopy and metabolic network tools, we analyzed the connections between the different metabolic switches activated by AICAR. Our approach reveals a strong interconnection between different phospholipid precursors and oxidation by-products. Metabolomics profiling is a useful tool for detecting major metabolic alterations, generating new hypotheses and provides some insight about the different molecular correlations in a complex system. The present study shows that AICAR induces metabolic effects in cell metabolism well beyond energy production pathways.     

Role of AMPK in skeletal muscle metabolic regulation and adaptation in relation to exercise

The 5'-AMP-activated protein kinase (AMPK) is a potent regulator of skeletal muscle metabolism and gene expression. AMPK is activated both in response to in vivo exercise and ex vivo contraction. AMPK is therefore believed to be an important signalling molecule in regulating muscle metabolism during exercise as well as in adaptation of skeletal muscle to exercise training. The first part of this review is focused on different mechanisms regulating AMPK activity during muscle work such as alterations in nucleotide concentrations, availability of energy substrates and upstream AMPK kinases. We furthermore discuss the possible role of AMPK as a master switch in skeletal muscle metabolism with the main focus on AMPK in metabolic regulation during muscle work. Finally, AMPK has a well established role in regulating expression of genes encoding various enzymes in muscle, and this issue is discussed in relation to adaptation of skeletal muscle to exercise training.     

Mechanisms underlying the temporal precision of sound coding at the inner hair cell ribbon synapse

AMP-activated protein kinase (AMPK) is involved in cellular energy homeostasis. Its functions have been extensively studied in muscles and liver. AMPK stimulates pathways which increase energy production (glucose transport, fatty acid oxidation) and switches off pathways which consume energy (lipogenesis, protein synthesis, gluconeogenesis). This has led to the concept that AMPK has an interesting pharmaceutical potential in situations of insulin resistance and it is indeed the target of existing drugs and hormones which improve insulin sensitivity. Adipose tissue is a key player in energy metabolism through the release of substrates and hormones involved in metabolism and insulin sensitivity. Activation of AMPK in adipose tissue can be achieved through situations such as fasting and exercise. Leptin and adiponectin as well as hypoglycaemic drugs are activators of adipose tissue AMPK. This activation probably involves changes in the AMP/ATP ratio and the upstream kinase LKB1. When activated, AMPK limits fatty acid efflux from adipocytes and favours local fatty acid oxidation. Since fatty acids have a key role in insulin resistance, especially in muscles, activating AMPK in adipose tissue might be found to be beneficial in insulin-resistant states, particularly as AMPK activation also reduces cytokine secretion in adipocytes.     

Fructose surges damage hepatic adenosyl-monophosphate-dependent kinase and lead to increased lipogenesis and hepatic insulin resistance

Fructose may be a key contributor to the biochemical alterations which promote the metabolic syndrome (MetS), non-alcoholic fatty liver disease (NAFLD) and type 2 diabetes (T2DM): (a) its consumption in all forms but especially in liquid form has much increased alongside with incidence of MetS conditions; (b) it is metabolized almost exclusively in the liver, where it stimulates de novo lipogenesis to drive hepatic triglyceride (TG) synthesis which (c) contributes to hepatic insulin resistance and NAFLD (Lustig et al., 2015; Weiss et al., 2013; Lim et al., 2010; Schwarzet al., 2015; Stanhope et al., 2009, 2013) [1–6]. The specifics of fructose metabolism and its main location in the liver serve to explain many of the possible mechanisms involved. It also opens questions, as the consequences of large increases in fructose flux to the liver may wreak havoc with the regulation of metabolism and would produce two opposite effects (inhibition and activation of AMP dependent kinase-AMPK) that would tend to cancel each other. We posit that (1) surges of fructose in the portal vein lead to increased unregulated flux to trioses accompanied by unavoidable methylglyoxal (MG) production, (2) the new, sudden flux exerts carbonyl stress on the three arginines on the γ subunits AMP binding site of AMPK, irreversible blocking some of the enzyme molecules to allosteric modulation, (3) this explains why, even when fructose quick phosphorylation increases AMP and should therefore activate AMPK, the effects of fructose are compatible with inactivation of AMPK, which then solves the apparent metabolic paradox. We put forward the hypothesis that fructose loads, via the increase in MG flux worsens the fructose-driven metabolic disturbances that lead to unrestricted de novo lipogenesis, fatty liver and hepatic insulin resistance. It does so via the silencing of AMPK. Our hypothesis is testable and if proven correct will shed some further light on fructose metabolism in the liver. It will also open new roads in glycation research, as modulation of MG catabolism may be a way to dampen the damage. Research on this area may have important therapeutic potential, e.g., more momentum to find new and improved carbonyl quenchers, new insights on the action of metformin, more evidence for the role of GAPDH inactivation due to mitochondrial overload in diabetes complications. AMPK plays a central role in metabolism, and its function varies in different tissues. For that reason, synthetic activators will always stumble with unwanted or unpredictable effects. Preventing MG damage on the protein could be a safer therapeutic avenue.     

Upregulation of AMPK during cold exposure occurs via distinct mechanisms in brown and white adipose tissue of the mouse

AMPK (adenosine monophosphate-activated protein kinase), a key regulator of cellular energy metabolism and whole-body energy balance, is present in brown adipose tissue but its role in regulating the acute metabolic state and chronic thermogenic potential of this metabolically unique tissue is unknown. To address this, the AMPK signalling system in brown and white adipose tissue was studied in C57Bl/6 mice under control conditions, during acute and chronic cold exposure, and during chronic adrenergic stimulation. In control mice AMPK activity in brown adipose tissue was higher than in any tissue yet reported (3-fold the level in liver) secondary to a high level of expression of the α1 isoform. During the first day of cold, a time of intense non-shivering thermogenesis, AMPK activity remained at basal levels. However, chronic (>7 days) cold caused a progressive increase in brown adipose tissue AMPK activity secondary to increased expression of the α1 isoform. To investigate the signalling pathway involved, noradrenaline (norepinephrine) and the β₃-adrenergic-specific agonist CL 316, 243 were given for 14 days. This increased uncoupling protein-1 content in brown adipose tissue, but not AMPK activity. In white adipose tissue 15 days of cold increased α1 AMPK activity 98 ± 20%, an effect reproduced by chronic noradrenaline or CL 316 243. We conclude that chronic cold not only increases AMPK activity in brown and white adipose tissue, but that it does so via distinct signalling pathways. Our data are consistent with AMPK acting primarily as a regulator of chronic thermogenic potential in brown adipose tissue, and not in the acute activation of non-shivering thermogenesis.     

FGF21 activates AMPK signaling: impact on metabolic regulation and the aging process

Fibroblast growth factor 21 (FGF21) has a significant role in the regulation of energy metabolism, e.g., in the control of systemic glucose and lipid metabolism. For instance, FGF21 enhances insulin sensitivity, increases glucose uptake, and thus can decrease serum hyperglycemia, while it also increases lipid oxidation and inhibits lipogenesis. AMP-activated protein kinase (AMPK) is a tissue energy sensor involved in maintaining the energy balance and tissue integrity. It is known that AMPK signaling generates an energy metabolic profile which displays a remarkable overlap with that of FGF21. There is convincing evidence that endocrine FGF21 signaling activates the AMPK pathway, either directly through FGFR1/β-klotho signaling or indirectly by stimulating the secretion of adiponectin and corticosteroids, which consequently can activate AMPK signaling in their target tissues. By activating AMPK, FGF21 can promote a healthy aging process and thus extend mammalian lifespan. We will examine the signaling mechanisms through which FGF21 can activate the AMPK pathway and then discuss the significance of the close connection between FGF21 and AMPK signaling in the control of metabolic disorders and the aging process.     

Role of hypothalamic 5′-AMP-activated protein kinase in the regulation of food intake and energy homeostasis

Although obesity is an epidemic threat to general health worldwide, an effective treatment has yet to be found. Insights into weight-regulatory pathways will accelerate the identification of new molecular targets for anti-obesity agents. 5-AMP-activated protein kinase (AMPK) is an enzyme activated during low cellular energy charge. In peripheral tissues, the activation of AMPK influences various metabolic pathways, including glucose uptake, glycolysis, and fatty acid oxidation, all of which help to re-establish a normal cellular energy balance. AMPK is also present in the neurons of the hypothalamus, a critical center in the regulation of energy homeostasis. Recent studies from our group and others have shown that many factors (-lipoic acid, leptin, insulin, ghrelin, glucose, 2-deoxyglucose, etc.) cause an alteration in hypothalamic AMPK activity that mediates effects on feeding behavior. Hypothalamic AMPK also appears to play a role in the central regulation of energy expenditure and peripheral glucose metabolism. These data indicate that hypothalamic AMPK is an important signaling molecule that integrates nutritional and hormonal signals and modulates feeding behavior and energy metabolism.     

Metabolic alterations and targeted therapies in prostate cancer

Cancer cells synthesize de novo large amounts of fatty acids and cholesterol, irrespective of the circulating lipid levels and benefit from this increased lipid synthesis in terms of growth advantage, self-survival and drug resistance. Key lipogenic alterations that commonly occur in prostate cancer include over-expression of the enzyme fatty acid synthase (FASN) and deregulation of the 5-AMP-activated protein kinase (AMPK). FASN is a key metabolic enzyme that catalyses the synthesis of palmitate from the condensation of malonyl-CoA and acetyl-CoA de novo and plays a central role in energy homeostasis, by converting excess carbon intake into fatty acids for storage. AMPK functions as a central metabolic switch that governs glucose and lipid metabolism. Recent interest has focused on the potential of targeting metabolic pathways that may be altered during prostate tumorigenesis and progression. Several small molecule inhibitors of FASN have now been described or in development for therapeutic use; in addition, drugs that directly or indirectly induce AMPK activation have potential benefit in prostate cancer prevention and treatment.     

AMP-activated protein kinase – development of the energy sensor concept

The LKB1→AMPK cascade is switched on by metabolic stresses that either inhibit ATP production (e.g. hypoxia, hypoglycaemia) or that accelerate ATP consumption (e.g. muscle contraction). Any decline in cellular energy status is accompanied by a rise in the cellular AMP: ATP ratio, and this activates AMPK by a complex and sensitive mechanism involving antagonistic binding of the nucleotides to two sites on the regulatory γ subunits of AMPK. Once activated by metabolic stress, AMPK activates catabolic pathways that generate ATP, while inhibiting cell growth and biosynthesis and other processes that consume ATP. While the AMPK system probably evolved in single-celled eukaryotes to maintain energy balance at the cellular level, in multicellular organisms its role has become adapted so that it is also involved in maintaining whole body energy balance. Thus, it is regulated by hormones and cytokines, especially the adipokines leptin and adiponectin, increasing whole body energy expenditure while regulating food intake. Some hormones may activate AMPK by an LKB1-independent mechanism involving Ca²⁺/calmodulin dependent protein kinase kinases. Low levels of activation of AMPK are likely to play a role in the current global rise in obesity and Type 2 diabetes, and AMPK is the target for the widely used antidiabetic drug metformin.     

Developing a head for energy sensing: AMP-activated protein kinase as a multifunctional metabolic sensor in the brain

The 5'-adenosine monophosphate-activated protein kinase (AMPK) is a metabolic and stress sensor that has been functionally conserved throughout eukaryotic evolution. Activation of the AMPK system by various physiological or pathological stimuli that deplete cellular energy levels promotes activation of energy restorative processes and inhibits energy consumptive processes. AMPK has a prominent role not only as a peripheral sensor of energy balance, but also in the CNS as a multifunctional metabolic sensor. Recent work suggests that AMPK plays an important role in maintaining whole body energy balance by coordinating feeding behaviour through the hypothalamus in conjunction with peripheral energy expenditure. In addition, brain AMPK is activated by energy-poor conditions induced by hypoxia, starvation, and ischaemic stroke. Under these conditions, AMPK is activated as a protective response in an attempt to restore cellular homeostasis. However in vivo, it appears that the overall consequence of activation of AMPK is more complex than previously imagined, in that over-activation may be deleterious rather than neuroprotective. This review discusses recent findings that support the role of AMPK in brain as a multidimensional energy sensor and the consequences of its activation or inhibition under physiological and pathological states.     

The role of metabolism in chondrocyte dysfunction and the progression of osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease characterized by low-grade inflammation and high levels of clinical heterogeneity. Aberrant chondrocyte metabolism is a response to changes in the inflammatory microenvironment and may play a key role in cartilage degeneration and OA progression. Under conditions of environmental stress, chondrocytes tend to adapt their metabolism to microenvironmental changes by shifting from one metabolic pathway to another, for example from oxidative phosphorylation to glycolysis. Similar changes occur in other joint cells, including synoviocytes. Switching between these pathways is implicated in metabolic alterations that involve mitochondrial dysfunction, enhanced anaerobic glycolysis, and altered lipid and amino acid metabolism. The shift between oxidative phosphorylation and glycolysis is mainly regulated by the AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) pathways. Chondrocyte metabolic changes are likely to be a feature of different OA phenotypes. Determining the role of chondrocyte metabolism in OA has revealed key features of disease pathogenesis. Future research should place greater emphasis on immunometabolism and altered metabolic pathways as a means to understand the pathophysiology of age-related OA. This knowledge will advance the development of new drugs against therapeutic targets of metabolic significance.     

LKB1 and AMPK: central regulators of lymphocyte metabolism and function

When T cells encounter foreign antigen and appropriate costimulatory signals from professional antigen-presenting cells (APCs), they initiate a coordinated program of rapid proliferation and differentiation, leading to the development of activated T cells with specific effector functions tailored toward pathogen clearance or control. One of the fundamental programs that underpin T-cell proliferation and function is the regulation of cellular metabolism. Recent efforts to identify the signal transduction pathways that regulate T-cell metabolism have led to the identification of liver kinase B1 (LKB1) and AMP-activated protein kinase (AMPK) as key regulators of T-cell metabolism. LKB1 and AMPK are part of an evolutionarily conserved signal transduction pathway that monitors cellular energy status. AMPK senses bioenergetic fluctuations in cells and works in concert with LKB1 to maintain cellular energy homeostasis by promoting catabolic pathways of ATP production and limiting processes that consume ATP. Recent data indicate that LKB1 and AMPK can influence diverse aspects of T-cell biology beyond metabolism, including T-cell development, peripheral T-cell homeostasis, and T-cell effector function. In this review, we focus on the regulation of lymphocyte metabolism by this energy-sensing pathway and discuss its influence on T-cell function.     

AMP-activated protein kinase (AMPK) controls the aging process via an integrated signaling network

Efficient control of energy metabolic homeostasis, enhanced stress resistance, and qualified cellular housekeeping are the hallmarks of improved healthspan and extended lifespan. AMPK signaling is involved in the regulation of all these characteristics via an integrated signaling network. Many studies with lower organisms have revealed that increased AMPK activity can extend the lifespan. Experiments in mammals have demonstrated that AMPK controls autophagy through mTOR and ULK1 signaling which augment the quality of cellular housekeeping. Moreover, AMPK-induced stimulation of FoxO/DAF-16, Nrf2/SKN-1, and SIRT1 signaling pathways improves cellular stress resistance. Furthermore, inhibition of NF-κB signaling by AMPK suppresses inflammatory responses. Emerging studies indicate that the responsiveness of AMPK signaling clearly declines with aging. The loss of sensitivity of AMPK activation to cellular stress impairs metabolic regulation, increases oxidative stress and reduces autophagic clearance. These age-related changes activate innate immunity defence, triggering a low-grade inflammation and metabolic disorders. We will review in detail the signaling pathways of this integrated network through which AMPK controls energy metabolism, autophagic degradation and stress resistance and ultimately the aging process.     

腺苷酸激活蛋白激酶在大鼠酒精性肝病中的表达减少

 【摘要】：目的：观察酒精对大鼠肝脏腺苷酸活化蛋白激酶（AMPK）表达水平的影响。方法：雄性Wistar大鼠50只,随机分出10只为正常对照组,其余动物采用酒精灌胃的方法,随机分为模型4、8、12、16周组,留取血清及肝组织标本;检测血清ALT、AST、CHE、TG、TC、LDL、VLD、HDL等生化指标,应用HE、天狼红及苏丹Ⅳ染色观察肝组织病理变化;应用免疫组织化学染色、RT-PCR法检测AMPK、ACC、SREBP蛋白及mRNA的表达。结果：随着酒精造模时间延长,血清ALT和AST水平逐渐升高,CHE水平逐渐降低;血清TG、TC、LDL水平逐渐升高,HDL水平逐渐降低;肝组织中AMPK表达逐渐减少,ACC及SREBP表达逐渐增多;肝组织AMPK与ACC及SREBP的表达呈负相关(r=-0.911, P<0.01; r=-0.907, P<0.01)。结论：ALD发病过程中AMPK表达减少,对ACC、SREBP活化的抑制作用减弱,脂质合成增多,造成脂肪堆积于肝脏中,是造成肝脏损伤的重要因素。AMPK作为一个新的药物靶点,为ALD的防治提供了新的思路。