Role of AMP-activated protein kinase gamma 3 genetic variability in glucose and lipid metabolism in non-diabetic whites

Aims/hypothesis AMP-activated protein kinase (AMPK) is a heterotrimeric enzyme that acts as an intracellular fuel sensor, directing multiple metabolic pathways in a catabolic direction in times of nutrient shortage. In humans, three different γ-subunits (γ₁, γ₂, γ₃) have been identified as AMPK regulators. The AMPKγ3 (protein kinase, AMP-activated, gamma 3 non-catalytic subunit, PRKAG3) isoform plays a role in gene regulation in glucose/lipid metabolism and skeletal muscle glycogen content. We investigated whether PRKAG3, in addition to being expressed in skeletal muscle, is also expressed in human liver. We also investigated whether genetic variance in PRKAG3 is associated with glucose and/or lipid metabolism in non-diabetic whites. Materials and methods After sequencing a screening cohort (n = 50) in the PRKAG3 locus, we genotyped 1061 participants for frequently found single nucleotide polymorphisms (SNPs). Association analyses between genotypes/haplotypes and metabolic traits were carried out. Results We detected PRKAG3 expression in human liver and skeletal muscle. Two SNPs (rs692243, rs6436094) with minor allele frequencies of 0.16 and 0.26 respectively and in moderate linkage disequilibrium (D′ = 0.92; r ² = 0.47) were found. rs692243 (C/G) confers a Pro71Ala mutation, while rs6436094 (A/G) is located in the 3′ untranslated region. No associations with prediabetic traits such as body fat distribution, insulin resistance or insulin secretion were found (p > 0.15 for all). However, the minor alleles of both SNPs were significantly associated with higher serum LDL-cholesterol and apolipoprotein (Apo) B-100 levels (rs692243: CG:LDL 4.3%, ApoB-100 3.4%; GG:LDL 7.6%, ApoB-100 5.4%; p = 0.008 and p = 0.01 respectively; rs6436094: AG:LDL 3.3%, ApoB-100 1.7%; GG:LDL 11.3%, ApoB-100 11.1%; p = 0.009 and p = 0.05 respectively; dominant model). The GG/GG diplotype homozygous for both minor SNP alleles displayed the highest LDL-cholesterol among all frequent diplotypes (p = 0.059). Conclusions/interpretation While genetic variability in PRKAG3 does not seem to have a major effect on glucose metabolism, it may play an important role in lipoprotein metabolism in humans.     

Apolipoprotein A-I stimulates AMP-activated protein kinase and improves glucose metabolism

Aims/hypothesis In humans, one of the hallmarks of type 2 diabetes is a reduced plasma concentration of HDL and its major protein component, apolipoprotein A-I (APOA-I). However, it is unknown whether APOA-I directly protects against diabetes. The aim of this study was to characterise the functional role of APOA-I in glucose homeostasis. Methods The effects of APOA-I on phosphorylation of AMP-activated protein kinase (AMPK) and acetyl-coenzyme A carboxylase (ACC), glucose uptake and endocytosis were analysed in C2C12 myocytes. Glucose metabolism was investigated in Apoa-I knockout (Apoa-I ^−/−) mice. Results APOA-I was able to stimulate the phosphorylation of AMPK and ACC, and elevated glucose uptake in C2C12 myocytes. APOA-I could be endocytosed into C2C12 myotubes through a clathrin-dependent endocytotic process. Inhibition of endocytosis abrogated APOA-I-stimulated AMPK phosphorylation. In Apoa-I ^−/− mice, AMPK phosphorylation was reduced in skeletal muscle and liver, and expression of gluconeogenic enzymes was increased in liver. In addition, the Apoa-I ^−/− mice had increased fat content and compromised glucose tolerance. Conclusions/interpretation Our data indicate that APOA-I has a protective effect against diabetes via activation of AMPK. ApoA-I deletion in the mouse led to increased fat mass and impaired glucose tolerance.     

AMP活化蛋白激酶的抗氧化作用

AMP活化蛋白激酶(AMPK)广泛参与细胞代谢,在调节细胞能量代谢过程中起重要作用.另外,AMPK还可以调节机体抗氧化能力,通过调节机体抗氧化防御系统蛋白的表达,如硫氧化还原蛋白(TRX)、NAD(P)H氧化酶、二氧化锰超氧化物歧化酶(MnSOD)、过氧化物酶体增殖物活化受体协同刺激因子(PGC)-1α等,减少机体活性...     

Mutation analysis of AMP-activated protein kinase subunits in inherited cardiomyopathies: implications for kinase function and disease pathogenesis

Familial hypertrophic cardiomyopathy (HCM) has been defined as a disease of the cardiac sarcomere, although sarcomeric protein mutations are not found in one third of cases. We have recently shown that HCM associated with Wolff-Parkinson-White syndrome (WPW) and conduction disease can be caused by mutations in PRKAG2, which encodes the gamma2 subunit of AMPK, an enzyme central to cellular energy homeostasis. AMPK is a heterotrimer composed of one catalytic subunit (alpha) and two regulatory subunits (beta and gamma). Seven known genes encode the subunit isoforms (alpha1, alpha2, beta1, beta2, gamma1, gamma2, gamma3) and all are expressed in the heart.To better understand the role of AMPK mutations in HCM/WPW and other inherited cardiomyophathies, all 7 subunit genes were screened for mutations in a panel of probands: 3 with HCM/WPW, 4 with DCM/WPW, 38 with HCM alone (in whom contractile protein mutations had not been found) and 13 with DCM alone. In total, 73 amplimers were screened in the 58 probands and a number of polymorphisms, including non-conservative substitutions, were identified. However, no further disease-causing mutations were found in any AMPK subunit gene.These results indicate that HCM with WPW is a distinct, but genetically heterogeneous, condition caused by mutations in PRKAG2 and in an unknown gene or genes, not involved in the AMPK complex. Mutations in PRKAG2 appear to specifically cause HCM with WPW and conduction disease, and not other inherited cardiomyopathies. As deleterious alleles were not found in other AMPK subunit isoforms, the mutations affecting PRKAG2 are likely to confer a specific alteration of AMPK function of particular importance in the myocardium.     

Targeting AMP-activated protein kinase as a novel therapeutic approach for the treatment of metabolic disorders

In the light of recent studies in humans and rodents, AMP-activated protein kinase (AMPK), a phylogenetically conserved serine/threonine protein kinase, has been described as an integrator of regulatory signals monitoring systemic and cellular energy status. AMP-activated protein kinase (AMPK) has been proposed to function as a 'fuel gauge' to monitor cellular energy status in response to nutritional environmental variations. Recently, it has been proposed that AMPK could provide a link in metabolic defects underlying progression to the metabolic syndrome. AMPK is a heterotrimeric enzyme complex consisting of a catalytic subunit and two regulatory subunits β and γ. AMPK is activated by rising AMP and falling ATP. AMP activates the system by binding to the γ subunit that triggers phosphorylation of the catalytic subunit by the upstream kinases LKB1 and CaMKKβ (calmodulin-dependent protein kinase kinase). AMPK system is a regulator of energy balance that, once activated by low energy status, switches on ATP-producing catabolic pathways (such as fatty acid oxidation and glycolysis), and switches off ATP-consuming anabolic pathways (such as lipogenesis), both by short-term effect on phosphorylation of regulatory proteins and by long-term effect on gene expression. As well as acting at the level of the individual cell, the system also regulates food intake and energy expenditure at the whole body level, in particular by mediating the effects of insulin sensitizing adipokines leptin and adiponectin. AMPK is robustly activated during skeletal muscle contraction and myocardial ischaemia playing a role in glucose transport and fatty acid oxidation. In liver, activation of AMPK results in enhanced fatty acid oxidation as well as decreased glucose production. Moreover, the AMPK system is one of the probable targets for the anti-diabetic drugs biguanides and thiazolidinediones. Thus, the relationship between AMPK activation and beneficial metabolic effects provide the rationale for the development of new therapeutic strategies in metabolic disorders.     

小檗碱的降糖作用独立于AMPK的信号通路

目的：研究小檗碱的降糖作用是否依赖于单磷酸腺苷激活蛋白激酶（AMPK）信号途径。方法培养HepG2细胞和C2C12细胞,给予不同浓度小檗碱处理。葡萄糖消耗实验和乳酸生成实验用于检测小檗碱的降糖以及刺激糖酵解的作用。AMPK抑制剂化合物C（Compound C,CC）和显性失活突变型AMPK,即腺病毒负显性AMPK（Ad-DN-AMPK）腺病毒用于抑制AMPK的表达和活性。Western印迹法用于检测AMPK以及乙酰辅酶A羧化酶（ACC）磷酸化水平,以评估AMPK通路的活性。结果小檗碱显著刺激了HepG2细胞和C2C12细胞的葡萄糖消耗和乳酸生成,并表现出剂量依赖性的药物作用。5和10μmol/L的小檗碱显著增加AMPK及其下游蛋白ACC的磷酸化水平。CC和Ad-DN-AMPK腺病毒转染能明显抑制细胞内AMPK信号通路的活性。然而,在AMPK活性被抑制的条件下,小檗碱依然能够显著增加细胞的葡萄糖消耗和乳酸生成。结论小檗碱通过刺激糖酵解而上调细胞的糖代谢,该作用无需AMPK信号通路的参与。即使在AMPK的表达或者活性被抑制的情况下,小檗碱依然能够发挥显著的降糖作用。     

Insulin resistance and improvements in signal transduction

Type 2 diabetes and obesity are common metabolic disorders characterized by resistance to the actions of insulin to stimulate skeletal muscle glucose disposal. Insulin-resistant muscle has defects at several steps of the insulin-signaling pathway, including decreases in insulin-stimulated insulin receptor and insulin receptor substrate-1 tyrosine phosphorylation, and phosphatidylinositol 3-kinase (Pl 3-kinase) activation. One approach to increase muscle glucose disposal is to reverse/improve these insulin-signaling defects. Weight loss and thiazolidinediones (TZDs) improve glucose disposal, in part, by increasing insulin-stimulated insulin receptor and IRS-1 tyrosine phosphorylation and PI 3-kinase activity. In contrast, physical training and metformin improve whole-body glucose disposal but have minimal effects on proximal insulin-signaling steps. A novel approach to reverse insulin resistance involves inhibition of the stress-activated protein kinase Jun N-terminal kinase (JNK) and the protein tyrosine phosphatases (PTPs). A different strategy to increase muscle glucose disposal is by stimulating insulin-independent glucose transport. AMP-activated protein kinase (AMPK) is an enzyme that works as a fuel gauge and becomes activated in situations of energy consumption, such as muscle contraction. Several studies have shown that pharmacologic activation of AMPK increases glucose transport in muscle, independent of the actions of insulin. AMPK activation is also involved in the mechanism of action of metformin and adiponectin. Moreover, in the hypothalamus, AMPK regulates appetite and body weight. The effect of AMPK to stimulate muscle glucose disposal and to control appetite makes it an important pharmacologic target for the treatment of type 2 diabetes and obesity.     

The role of AMP-activated protein kinase in regulating white adipose tissue metabolism

AMP-activated protein kinase (AMPK) is a heterotrimeric enzyme that plays a major role in the maintenance of energy homeostasis in various organs and tissues. When activated, AMPK can induce substrate catabolism and shut down energy-consuming anabolic pathways to increase intracellular ATP availability. Even though most of these effects have been described in muscle and liver, several studies have provided compelling evidence that AMPK also plays an important role in the regulation of white adipose tissue (WAT) glucose and lipid metabolism. In fact, the effects of acute and chronic AMPK activation in the WAT induce profound changes in adiposity with important implications for the treatment of obesity and its related metabolic disorders. This review discusses the role of AMPK in the regulation of white adipocyte metabolism with respect to energy storage and release, gene expression, mitochondrial biogenesis, oxidative capacity, cell differentiation, and the potential impact on whole-body adiposity and energy homeostasis.     

Emerging role of AMP-activated protein kinase in endocrine control of metabolism in the liver

This review summarizes the emerging role of AMP-activated protein kinase (AMPK) in mediating endocrine regulation of metabolic fluxes in the liver. There are a number of hormones which, when acting on the liver, alter AMPK activation. Here we describe those hormones associated with activation and de-activation of AMPK and the potential mechanisms for changes in AMPK activation state. The actions of these hormones, in many cases, are consistent with downstream effects of AMPK signaling thus strengthening the circumstantial case for AMPK-mediated hormone action. In recent years, genetic mouse models have also been used in an attempt to establish the role of AMPK in hormone-stimulated metabolism in the liver. Few experiments have, however, firmly established a causal relationship between hormone action at the liver and AMPK signaling.     

Sodium–glucose cotransporter inhibition: therapeutic potential for the treatment of type 2 diabetes mellitus

Results from randomized controlled trials have demonstrated that the risk of microvascular complications can be reduced by intensive glycaemic control in patients with type 2 diabetes mellitus (T2DM). However, only about half of patients with diagnosed diabetes achieve recommended glycaemic goals. New therapies with complementary mechanisms of action that are independent of insulin secretion or action may provide additional therapeutic options to enable patients to achieve glycaemic control. The kidney plays an important role in glucose homeostasis, primarily by the reabsorption of filtered glucose. The sodium–glucose cotransporter 2 (SGLT2), located in the proximal convoluted tubule, is responsible for the majority of glucose reabsorption by the kidney. SGLT2 inhibitors offer a novel approach to treat T2DM and reduce hyperglycaemia by increasing urinary excretion of glucose. Dapagliflozin, an SGLT2 inhibitor recently approved in Europe for the treatment of T2DM, improves glycaemic control in patients with T2DM when used as monotherapy or when added to other diabetes medications, such as metformin, sulfonylureas, pioglitazone, and insulin. As a class, SGLT2 inhibitors are well tolerated and have a low propensity to cause hypoglycaemia. An increase in signs, symptoms, and other events suggestive of genital and, in some studies, urinary tract infections has been reported with SGLT2 inhibitors. Results from ongoing and future clinical trials will help define the role for this new class of investigational compounds, with its unique mechanism of action, as a treatment option for reducing hyperglycaemia in patients with T2DM. Copyright © 2013 John Wiley & Sons, Ltd.     

Exercise lowers postprandial glucose but not fasting glucose in type 2 diabetes: a meta‐analysis of studies using continuous glucose monitoring

Exercise has repeatedly been shown to improve glycemic control as assessed by glycated hemoglobin. However, changes in glycated hemoglobin do not provide information regarding which aspects of glycemic control have been altered. The purpose of this systematic review was to examine the effect of exercise as assessed by continuous glucose monitoring systems (CGMS) in type 2 diabetes. Databases (PubMed, Medline, EMBASE) were searched up to February 2013. Eligible studies had participants with type 2 diabetes complete standardized exercise protocols and used CGMS to measure changes in glycemic control. Randomized controlled trials, crossover trials and studies with pre‐post designs were included. Average glucose concentration, daily time spent in hyperglycemia or hypoglycemia, and fasting glucose concentration were compared between exercise and control conditions. Eleven studies met the inclusion criteria and were included in the review. Eight studies had short‐term (≤2 weeks) exercise interventions, whereas three studies had a longer‐term intervention (all >2 months). The types of exercises utilized included aerobic, resistance and a combination of the two. The eight short‐term studies were included in quantitative analysis. Exercise significantly decreased average glucose concentrations (‐0.8 mmol/L, p < 0.01) and daily time spent in hyperglycemia (‐129 minutes, p < 0.01), but did not significantly affect daily time spent in hypoglycemia (‐3 minutes, p = 0.47) or fasting glucose (‐0.3 mmol/L, p = 0.13). The four randomized crossover trials had similar findings compared to studies with pre‐post designs. Exercise consistently reduced average glucose concentrations and time spent in hyperglycemia despite not significantly affecting outcomes such as fasting glucose and hypoglycemia. Copyright © 2013 John Wiley & Sons, Ltd.     

Glycaemic variability: The under-recognized therapeutic target in type 1 diabetes care

Type 1 diabetes mellitus (T1DM) remains one of the most challenging long-term conditions to manage. Despite robust evidence to demonstrate that near normoglycaemia minimizes, but does not completely eliminate, the risk of complications, its achievement has proved almost impossible in a real-world setting. HbA1c to date has been used as the gold standard marker of glucose control and has been shown to reflect directly the risk of diabetes complications. However, it has been recognized that HbA1c is a crude marker of glucose control. Continuous glucose monitoring (CGM) provides the ability to measure and observe inter- and intraday glycaemic variability (GV), a more meaningful measure of glycaemic control, more relevant to daily living for those with T1DM. This paper reviews the relationship between GV and hypoglycaemia, and micro- and macrovascular complications. It also explores the impact on GV of CGM, insulin pumps, closed-loop technologies, and newer insulins and adjunctive therapies. Looking to the future, there is an argument that GV should become a key determinant of therapeutic success. Further studies are required to investigate the pathological and psychological benefits of reducing GV.     

The effects and acceptability of different exercise modes on glycemic control in type 2 diabetes mellitus: A protocol for systematic review and network meta-analysis

Introduction:Exercise has been believed to have positive effects on blood glucose control in patients with type 2 diabetes mellitus. However, few medical evidences have been found to ascertain which type of exercise has the best effect on blood glucose control in diabetes and which type of exercise is more acceptable. The purpose of this study is to compare the effects and acceptability of different exercise modes on glycemic control in type 2 diabetes patients by using systematic review and network meta-analysis.Methods and analysis:Relevant randomized controlled trial studies will be searched from PubMed, EMbase, CochraneCENTRAL, CNKI, VIP, and Chinese medical paper libraries. Primary outcome indicators: glycosylated hemoglobin and dropout rate of the research (number of dropouts/numbers of initially enrolled subjects). Secondary outcome measures: fasting blood glucose, body weight, total cholesterol (TC), low-density lipoprotein cholesterol (LDL), high-density lipoprotein cholesterol, triglycerides (TG), diastolic pressure, systolic pressure (SBP). Two reviewers are arranged to screen Title, Abstract, and then review full text to further extract data. Standard meta-analysis and network meta-analysis of the data are performed afterward. Methodological quality assessment is planned to be conducted using Cochrane risk of bias tool. The outcome will be analyzed statistically according to Bayesian analysis methods. After that, subgroup analysis is conducted on the duration of intervention, whether there is supervision of intervention, frequency of intervention per week, age, gender, and medication use.Trial registration number:PROSPERO CRD42020175181Discussion:The systematic review and network meta-analysis include evidence of the impact of different exercise modes on blood glucose control in type 2 diabetes mellitus. There are 2 innovative points in this study. One is to conduct a classified study on exercise in as much detail as possible, and the other is to study the acceptability of different exercise modes. The network meta-analysis will reduce the uncertainty of intervention and enable clinicians, sports practitioners, and patients to choose more effective and suitable exercise methods.Ethics and dissemination:The findings of the study will be disseminated through publications in peer-reviewed journals and scientific conferences and symposia. Further, no ethical approval is required in this study.     

二甲双胍和饮食因素对糖尿病小鼠骨骼肌AMPK活性的影响

将2型糖尿病KK-Ay小鼠分为二甲双胍／高脂饮食、二甲双胍／低脂饮食、高脂饮食和低脂饮食4组，通过测定骨骼肌中腺苷酸活化蛋白激酶（AMPK）活性，发现二甲双胍和低脂饮食均可使AMPK活性增加，二者不存在累加效应。     

Age-related changes in AMP-activated protein kinase after stroke

Adenosine monophosphate-activated protein kinase (AMPK) is an evolutionary conserved energy sensor sensitive to changes in cellular AMP/ATP ratio which is activated by phosphorylation (pAMPK). pAMPK levels decrease in peripheral tissues with age, but whether this also occurs in the aged brain, and how this contributes to the ability of the aged brain to cope with ischemic stress is unknown. This study investigated the activation of AMPK and the response to AMPK inhibition after induced stroke in both young and aged male mice. Baseline levels of phosphorylated AMPK were higher in aged brains compared to young mice. Stroke-induced a robust activation of AMPK in young mice, yet this response was muted in the aged brain. Young mice had larger infarct volumes compared with aged animals; however, more severe behavioral deficits and higher mortality were seen in aged mice after stroke. Inhibition of AMPK with Compound C decreased infarct size in young animals, but had no effect in aged mice. Compound C administration led to a reduction in brain ATP levels and induced hypothermia, which led to enhanced neuroprotection in young but not aged mice. This work demonstrates that aging increases baseline brain pAMPK levels; aged mice have a muted stroke-induced pAMPK response; and that AMPK inhibition and hypothermia are less efficacious neuroprotective agents in the aged brain. This has important translational relevance for the development of neuroprotective agents in preclinical models and our understanding of the enhanced metabolic stress experienced by the aged brain.     

Exercise increases skeletal muscle GLUT4 gene expression in patients with type 2 diabetes

The aim of the study was to determine the effect of a single bout of exercise on GLUT4 gene expression in muscle of patients with type 2 diabetes (T2D) and control subjects, matched for age and body mass index. Nine patients with T2D and nine control subjects performed 60 min of cycling exercise at ~55% peak power (W(max) ). Skeletal muscle biopsies were obtained at baseline, immediately post and 3-h post exercise. GLUT4 mRNA expression increased (p < 0.05) to a similar extent immediately post exercise in control (~60%) and T2D (~66%) subjects, and remained elevated (p < 0.05) 3-h post exercise with no differences between groups. Similarly, p-AMP-activated protein kinase, p38 mitogen-activated kinase and proliferator-activated receptor gamma co-activator-alpha mRNA expression were increased (p < 0.05) post exercise, and were not different between the groups. In conclusion, a single bout of exercise increased skeletal muscle GLUT4 mRNA expression in patients with T2D to a similar extent as in control subjects.