AMPK: positive and negative regulation, and its role in whole-body energy homeostasis

Astragaloside IV Inhibits Triglyceride Accumulation in Insulin-Resistant HepG2 Cells via AMPK-Induced SREBP-1c Phosphorylation

Objective: Insulin resistance (IR) is a risk factor for non-alcoholic fatty liver disease (NAFLD), which is characterized by lipid accumulation in hepatocytes. AMP-activated protein kinase (AMPK)-induced sterol regulatory element binding protein-1c (SREBP-1c) phosphorylation is crucial for proper regulation of lipid metabolism in the liver. Astragaloside IV (AST-IV) was found to decrease lipid accumulation in hepatocytes by activating AMPK, which is required to regulate lipid metabolism in liver tissue by inducing SREBP-1c phosphorylation.

Method: To evaluate the direct effect of AST on lipid accumulation in hepatocytes with IR and elucidate the underlying mechanisms, we induced IR in HepG2 cells, and used compound C and 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) (an AMPK inhibitor and agonist, respectively) as control substances. We evaluated glucose, triglyceride (TG), and non-esterified fatty acid (NEFA) production, as well as SREBP-1c transcription, SREBP-1c protein expression, and downstream gene expression with or without the presence of AST. We also investigated whether phosphorylation of SREBP-1c at Ser372 was required for AST function.

Results: We found that AST attenuated IR and lipid accumulation in HepG2 cells. As an AMPK activator, AST promoted gene expression and activation of AMPK by increasing phosphorylation of AMPKa. AST also inhibited translocation of SREBP-1c into the nucleus of insulin-resistant HepG2 cells by inducing phosphorylation of SREBP-1c at Ser372.

Conclusion: This study demonstrated that AST attenuates IR and lipid accumulation in HepG2 cells by regulating AMPK-dependent phosphorylation of SREBP-1c at Ser372, suggesting AST as a promising drug for treating hepatic steatosis.

Effects of interleukin-6 and IL-6/AMPK signaling pathway on mitochondrial biogenesis and astrocytes viability under experimental septic condition

OBJECTIVE

Interleukin-6 (IL-6) is a neuromodulation factor with extensive and complex biological activities. IL-6 has been reported to activate AMPK, while AMPK regulates mitochondrial biogenesis and autophagy. The aim of this study was to investigate the role of IL-6 in mitochondrial biogenesis using astrocytes under experimental septic condition and examined how IL-6/AMPK signaling pathway affected this process.

METHODS

The primary cultures of cerebral cortical astrocytes were randomly allocated into six groups: control group, LPS+IFN-γ group, IL-6 group (LPS+IFN-γ+IL-6), C group (LPS+IFN-γ+IL-6+Compound C), siRNA group (LPS+IFN-γ+IL-6+IL-6R siRNA) and siRNA+C group (LPS+IFN-γ+IL-6+IL-6R siRNA+ Compound C). All groups were stimulated for 6 h. Cytokines and reactive oxygen species (ROS) analyses, detection of adenosine triphosphate (ATP), mtDNA content and cell viability, evaluation of the mitochondrial ultrastructure and volume density, western blots of proteins associated with mitochondrial biogenesis and phospho-adenosine monophosphate activated protein kinase (p-AMPK) were performed respectively.

RESULTS

Compared with LPS+IFN-γ group, IL-6 group had milder ultrastructural damage of mitochondria, higher mtDNA content and mitochondrial volume density, higher expression of proteins associated with mitochondrial biogenesis (PGC-1α, NRF-1 and TFAM) and p-AMPK, and thus higher cell viability, whereas blocking IL-6/AMPK signaling pathway, the protective effect of IL-6 has been diminished, compared with IL-6 group.

CONCLUSION

IL-6 enhances mitochondrial biogenesis in astrocytes under experimental septic condition through IL-6/AMPK signaling pathway.

Structural Determinants for Small-Molecule Activation of Skeletal Muscle AMPK α2β2γ1 by the Glucose Importagog SC4

The AMP-activated protein kinase (AMPK) αβγ heterotrimer regulates cellular energy homeostasis with tissue-specific isoform distribution. Small-molecule activation of skeletal muscle α2β2 AMPK complexes may prove a valuable treatment strategy for type 2 diabetes and insulin resistance. Herein, we report the small-molecule SC4 is a potent, direct AMPK activator that preferentially activates α2 complexes and stimulates skeletal muscle glucose uptake. In parallel with the term secretagog, we propose "importagog" to define a substance that induces or augments cellular uptake of another substance. Three-dimensional structures of the glucose importagog SC4 bound to activated α2β2γ1 and α2β1γ1 complexes reveal binding determinants, in particular a key interaction between the SC4 imidazopyridine 4'-nitrogen and β2-Asp111, which provide a design paradigm for β2-AMPK therapeutics. The α2β2γ1/SC4 structure reveals an interaction between a β2 N-terminal α helix and the α2 autoinhibitory domain. Our results provide a structure-function guide to accelerate development of potent, but importantly tissue-specific, β2-AMPK therapeutics.

Ocimum basilicum but not Ocimum gratissimum present cytotoxic effects on human breast cancer cell line MCF-7, inducing apoptosis and triggering mTOR/Akt/p70S6K pathway

Breast cancer is the major cause of death by cancer in women worldwide and in spite of the many drugs for its treatment, there is still the need for novel therapies for its control. Ocimum species have been used by traditional medicine to control several diseases, including cancer. We have previously characterized the antidiabetic properties of the unfractionated aqueous leaf extracts of Ocimum basilicum (OB) and Ocimum gratissimum (OG), modulating glucose metabolism in diabetic mice. Since glucose metabolism is primordial for cancer cells survival, we hypothesized that these extracts are effective against cancer cells. The unfractionated aqueous leaf extracts of OB and OG were chemically characterized and tested for their cytotoxic, cytostatic and anti-proliferative properties against the human breast cancer cell line MCF-7. Both extracts presented cytostatic effects with an 80% decrease in MCF-7 cell growth at 1 mg/mL. However, only OB promoted cytotoxic effects, interfering with the cell viability even after interruption of the treatment. Moreover, OB but not OG affected the cell proliferation and metabolism, evaluated in terms of lactate production and intracellular ATP content. After 24 h of treatment, OB treated cells presented an apoptotic profile, while OG treated cells were more necrotic. The treatment with both extracts also activated AMPK, but OB was much more efficient than OG in promoting this. The activation of mTOR signaling, another survival pathway was promoted by OB, whereas OG failed to activate it. In the end, we conclude that OB extract is efficient against the human breast cancer cell line.

An in vitro comparative study of the antioxidant activity and SIRT1 modulation of natural compounds

Oxidative stress arises from an imbalance between the production of free radicals and antioxidant defences. Several studies have suggested that dietary antioxidants (such as polyphenols and berberine) may counteract oxidative stress through the involvement of the Sirtuin 1/Adenosine Monophosphate-Activated Protein Kinase (SIRT1/AMPK) pathway. The aim of this study was to evaluate the direct and specific antioxidant activity of some natural compounds, as well as their ability to modulate the expression of SIRT1 and the activation of AMPK. Quercetin, tyrosol, ferulic acid, catechin, berberine and curcumin were evaluated for their specific and direct antioxidant activity with TOSC assay. Their ability to modulate SIRT1 and AMPK was assessed by immunoblotting assay, while their cytotoxicity by CellTiter-Blue Cell Viability Assay. No statistically significant decrease (p > 0.05) in the number of viable cells was found upon challenging with the natural compounds. Quercetin exhibited the highest antioxidant activity against peroxyl radical and peroxinitrate derivates, while curcumin showed the best anti-hydroxyl activity with respect to the other compounds and, most importantly, respect to the reference antioxidants. Finally, all the tested compounds significantly increased the SIRT1 expression and the activation of AMPK. Our results clearly disclose the specific antioxidant activity of these natural compounds and their ability to increase SIRT1 expression and AMPK activation.

AMPK-Akt Double-Negative Feedback Loop in Breast Cancer Cells Regulates Their Adaptation to Matrix Deprivation

Cell detachment from the extracellular matrix triggers anoikis. Disseminated tumor cells must adapt to survive matrix deprivation, while still retaining the ability to attach at secondary sites and reinitiate cell division. In this study, we elucidate mechanisms that enable reversible matrix attachment by breast cancer cells. Matrix deprival triggered AMPK activity and concomitantly inhibited AKT activity by upregulating the Akt phosphatase PHLPP2. The resultant pAMPKhigh/pAktlow state was critical for cell survival in suspension, as PHLPP2 silencing also increased anoikis while impairing autophagy and metastasis. In contrast, matrix reattachment led to Akt-mediated AMPK inactivation via PP2C-α-mediated restoration of the pAkthigh/pAMPKlow state. Clinical specimens of primary and metastatic breast cancer displayed an Akt-associated gene expression signature, whereas circulating breast tumor cells displayed an elevated AMPK-dependent gene expression signature. Our work establishes a double-negative feedback loop between Akt and AMPK to control the switch between matrix-attached and matrix-detached states needed to coordinate cell growth and survival during metastasis.Significance: These findings reveal a molecular switch that regulates cancer cell survival during metastatic dissemination, with the potential to identify targets to prevent metastasis in breast cancer. Cancer Res; 78(6); 1497-510. ©2018 AACR.

Potential Roles of Dec and Bmal1 Genes in Interconnecting Circadian Clock and Energy Metabolism

The daily rhythm of mammalian energy metabolism is subject to the circadian clock system, which is made up of the molecular clock machinery residing in nearly all cells throughout the body. The clock genes have been revealed not only to form the molecular clock but also to function as a mediator that regulates both circadian and metabolic functions. While the circadian signals generated by clock genes produce metabolic rhythms, clock gene function is tightly coupled to fundamental metabolic processes such as glucose and lipid metabolism. Therefore, defects in the clock genes not only result in the dysregulation of physiological rhythms but also induce metabolic disorders including diabetes and obesity. Among the clock genes, Dec1 (Bhlhe40/Stra13/Sharp2), Dec2 (Bhlhe41/Sharp1), and Bmal1 (Mop3/Arntl) have been shown to be particularly relevant to the regulation of energy metabolism at the cellular, tissue, and organismal levels. This paper reviews our current knowledge of the roles of Dec1, Dec2, and Bmal1 in coordinating the circadian and metabolic pathways.

Caloric Restriction Dramatically Stalls Lesion Growth in Mice With Induced Endometriosis

Caloric restriction (CR) has been demonstrated to have many health-beneficial effects in many species, but whether CR can impede the development of endometriosis is unknown. To test the hypothesis that CR can impede the growth of endometriotic lesions and fibrogenesis, we conducted 2 experiments. In experiment 1, 20 female Balb/C mice were randomly assigned to either ad libitum (AL) group that was fed AL or to CR group that was fed 30% less calories than that of AL mice. Two weeks after the implementation of the dietary intervention, endometriosis was induced by intraperitoneal injection of endometrial fragments. Two weeks after the induction, all mice were sacrificed and their lesion samples were evaluated. In experiment 2, another 20 mice were used and CR was implemented 2 weeks after induction of endometriosis and lasted for 4 weeks. Caloric restriction instituted before the induction of endometriosis reduced the lesion weight by 88.5%, whereas CR implemented well after lesions were established reduced the lesion weight by 93.0%. In both cases, CR significantly increased staining levels of markers of autophagy but reduced proliferation, angiogenesis, steroidogenesis, and fibrosis in lesions as compared with the AL group. Consequently, CR, instituted either before or after the induction of endometriosis, dramatically curbs the growth of endometriotic lesions and fibrogenesis through multiple mechanisms. Caloric restriction and CR mimetics, a family of compounds mimicking the beneficial effect of CR, even when instituted well after lesions are established, may stall the development of endometriosis. Given the scarcity in research on how lifestyle can impact on the development of endometriosis, our study should hopefully stimulate more research in this area.

Sexual dimorphism in activation of placental autophagy in obese women with evidence for fetal programming from a placenta-specific mouse model

The incidence of maternal obesity and its co-morbidities (diabetes, cardiovascular disease) continues to increase at an alarming rate, with major public health implications. In utero exposure to maternal obesity has been associated with development of cardiovascular and metabolic diseases in the offspring as a result of developmental programming. The placenta regulates maternal-fetal metabolism and shows significant changes in its function with maternal obesity. Autophagy is a cell-survival process, which is responsible for the degradation of damaged organelles and misfolded proteins. Here we show an activation of autophagosomal formation and autophagosome-lysosome fusion in placentas of males but not females from overweight (OW) and obese (OB) women vs. normal weight (NW) women. However, total autophagic activity in these placentas appeared to be decreased as it showed an increase in SQSTM1/p62 and a decrease in lysosomal biogenesis. A mouse model with a targeted deletion of the essential autophagy gene Atg7 in placental tissue showed significant placental abnormalities comparable to those seen in human placenta with maternal obesity. These included a decrease in expression of mitochondrial genes and antioxidants, and decreased lysosomal biogenesis. Strikingly, the knockout mice were developmentally programmed as they showed an increased sensitivity to high-fat diet-induced obesity, hyperglycemia, hyperinsulinemia, increased adiposity, and cardiac remodeling. In summary, our results indicate a sexual dimorphism in placental autophagy in response to maternal obesity. We also show that autophagy plays an important role in placental function and that inhibition of placental autophagy programs the offspring to obesity, and to metabolic and cardiovascular diseases.

The Two Translationally Controlled Tumor Protein Genes, CsTCTP1 and CsTCTP2, Are Negative Modulators in the Cucumis sativus Defense Response to Sphaerotheca fuliginea

Pathogen stress often significantly decreases cucumber production. However, knowledge regarding the molecular mechanism and signals of cucumber disease resistance is far from complete. Here, we report two translationally controlled tumor protein genes, CsTCTP1 and CsTCTP2, that are both negative modulators in the Cucumis sativus defense response to Sphaerotheca fuliginea. Subcellular localization analysis showed that CsTCTP1 and CsTCTP2 were both localized in the cytoplasm. Expression analysis indicated that the transcript levels of CsTCTP1 and CsTCTP2 were linked to the degree of cucumber resistance to S. fuliginea. Transient overexpression of either CsTCTP1 or CsTCTP2 in cucumber cotyledons impaired resistance to S. fuliginea, whereas silencing of either CsTCTP1 or CsTCTP2 enhanced cucumber resistance to S. fuliginea. The relationship of several defense-related genes and ABA and target of rapamycin (TOR) signaling pathway-related genes to the overexpressing and silencing of CsTCTP1/CsTCTP2 in non-infested cucumber plants was investigated. The results indicated that CsTCTP1 participates in the defense response to S. fuliginea by regulating the expression of certain defense-associated genes and/or ABA signaling pathway-associated genes, and CsTCTP2 participates through regulating the expression of TOR signaling pathway-associated genes. Our findings will guide enhancing the resistance of cucumber to powdery mildew.

Metformin, an Anti-diabetic Drug to Target Leukemia

Metformin, a widely used anti-diabetic molecule, has attracted a strong interest in the last 10 years as a possible new anti-cancer molecule. Metformin acts by interfering with mitochondrial respiration, leading to an activation of the AMPK tumor-suppressive pathway to promote catabolic-energy saving reactions and block anabolic ones that are associated with abnormal cell proliferation. Metformin also acts at the organism level. In type 2 diabetes patients, metformin reduces hyperglycemia and increases insulin sensitivity by enhancing insulin-stimulated glucose uptake in muscles, liver, and adipose tissue and by reducing glucose output by the liver. Lowering insulin and insulin-like growth factor 1 (IGF-1) levels that stimulate cancer growth could be important features of metformin's mode of action. Despite continuous progress in treatments with the use of targeted therapies and now immunotherapies, acute leukemias are still of very poor prognosis for relapse patients, demonstrating an important need for new treatments deriving from the identification of their pathological supportive mechanisms. In the last decade, it has been realized that if cancer cells modify and reprogram their metabolism to feed their intense biochemical needs associated with their runaway proliferation, they develop metabolic addictions that could represent attractive targets for new therapeutic strategies that intend to starve and kill cancer cells. This Mini Review explores the anti-leukemic potential of metformin and its mode of action on leukemia metabolism.

Studies on prevention of obesity, metabolic syndrome, diabetes, cardiovascular diseases and cancer by tea

Tea, a popular beverage made from leaves of the plant Camellia sinensis, has been studied extensively in recent decades for its beneficial health effects in the prevention of obesity, metabolic syndrome, diabetes, cancer, and other diseases. Whereas these beneficial effects have been convincingly demonstrated in most laboratory studies, results from human studies have not been consistent. Some studies demonstrated that weight reduction, alleviation of metabolic syndrome and risk reduction in diabetes were only observed in individuals who consume 3-4 cups of tea (600-900 mg tea catechins) or more daily. This chapter reviews some of these studies, the possible mechanisms of actions of tea constituents, and the challenges in extrapolating laboratory studies to human situations.

ATM signals to AMPK to promote autophagy and positively regulate DNA damage in response to cadmium-induced ROS in mouse spermatocytes

Cadmium (Cd) is a toxic heavy metal and harmful to human health due to its ability to accumulate in organs. Previous studies have shown that Cd can induce DNA damage and autophagy. Autophagy can stabilize genetic material and DNA integrity. The aim of the present study was to determine the exact mechanism and role of autophagy induced by Cd in spermatozoa cells. Mouse spermatocyte-derived cells (GC-2) were treated with 20 μM Cd chloride for 24 h. The level of reactive oxygen species (ROS), DNA damage, autophagy and the expression of the molecular signaling pathway ATM/AMP-activated protein kinase (AMPK)/mTOR were determined. The results showed that Cd induced autophagy and DNA damage in GC-2 cells via ROS generation, and the autophagy signal pathway AMPK/mTOR was activated by ATM which is a DNA damage sensor. Melatonin, a well-known antioxidant, ameliorated DNA damage, and inhibited autophagy via the AMPK/mTOR signal pathway. Furthermore, after inhibition of autophagy by knockdown of AMPKα, increased DNA damage by Cd treatment was observed in GC-2 cells. These findings demonstrated the protective role of autophagy in DNA damage and suggested that the mechanism of autophagy induced by Cd was through the ATM/AMPK/mTOR signal pathway in spermatozoa cells.

AMPK downregulates ALK2 via increasing the interaction between Smurf1 and Smad6, leading to inhibition of osteogenic differentiation

Activin A receptor type I or activin receptor-like kinase 2 (ACVRI/ALK2) belongs to type I TGF-β family and plays an important role in bone development. Activating mutations of ALK2 containing the R206 to H mutation, are present in 95% in the rare autosomal genetic disease fibrodysplasia ossificans progressiva (FOP), which leads to the development of ectopic bone formation in muscle. The effect of AMP-activated protein kinase (AMPK) activation on ALK2R206H-mediated signaling in fibroblasts obtained from a FOP patient was assessed in the present study. The activity of the mutated ALK2 was suppressed by pharmacological AMPK activators such as metformin and aspirin, while their actions were blocked by the dominant negative mutant of AMPK and mimicked by the constitutively active mutant of AMPK. Furthermore, activation of AMPK upregulated Smad6 and Smurf1 and thereby enhanced their interactions, resulting in its proteosome-dependent degradation of ALK2. In contrast, knockdown of Smad6 or Smurf1 prevented metformin-induced reduction of ALK2. To evaluate the biological relevance of AMPK action on ALK2 activity, we induced FOP fibroblasts into iPS cells and found that their osteogenic differentiation in vitro was inhibited by metformin. Our studies provide novel insight into potential approaches to treatment of FOP, since several AMPK activators (e.g. metformin, berberine, and aspirin) are already in clinical use for the treatment of diabetes and metabolic syndromes.

Formaldehyde alters triglyceride synthesis and very low-density lipoprotein secretion in a time-dependent manner

Formaldehyde is a common indoor air pollutant that is toxic to the liver. This study aimed to investigate the effects of formaldehyde on triglyceride metabolism in human hepatocellular carcinoma cells (HepG2). Cell viability was detected using a MTT (3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide) assay. Following treatment with different concentrations of formaldehyde for 24 and 48h, the intra and extra-hepatocellular triglyceride (TG) content was determined using a chemical-enzymatic method; Western blotting was used to detect the levels of fatty acid synthesis and VLDL-related proteins. Our results showed that cell viability significantly decreased after formaldehyde treatment (0.5-12.5mM, 24/48h). Extracellular TG levels in the hepatocytes increased after formaldehyde treatment at 0.004mM-0.1mM for 24h. SREBP-1c, ACC, FASN, and MTP, CES3 and DGAT1 proteins increased significantly after 24h of formaldehyde treatment. Intracellular TG levels decreased for 48h treatment of formaldehyde. AMPKα increased significantly in all tested groups and p-AMPK increased significantly after 0.1mM formaldehyde treatment for 48h. Our results indicated that short-term formaldehyde exposure balances triglyceride metabolism by promoting hepatocellular TG synthesis and VLDL secretion; Long-term formaldehyde disturbs the TG metabolism balance in the hepatocytes.

PDGFR Signaling Mediates Hyperproliferation and Fibrotic Responses of Subsynovial Connective Tissue Cells in Idiopathic Carpal Tunnel Syndrome

Fibrosis of the subsynovial connective tissue (SSCT) is a pathognomonic change in carpal tunnel syndrome (CTS). Identification of molecular targets and anti-fibrotic therapies could provide new treatment strategies for CTS. The contribution of SSCT cells to fibrosis and the signaling pathways that initiate and aggravate fibrosis in CTS remain unknown. Here we report that platelet-derived growth factor receptor alpha (PDGFRα) positive ( + ) cells accumulate in CTS SSCT and that the presence of fibrotic growth factor, PDGF-AA, results in increased proliferation of PDGFRα+ cells via PI3K/Akt signaling pathway. Although PI3K inhibition decreased proliferation, there was no change in fibrosis-related gene expression. Indeed, protein levels of fibrosis signaling mediator TGF-β remained the same and the second messenger, Smad2/3, accumulated in the nucleus. In contrast AMP-activated protein kinase (AMPK) activation, which can be induced with metformin and AICAR inhibited proliferation, TGF-β expression, and altered cell morphology in SSCT cells. Further we show that AMPK activation by metformin reduced collagen III levels and the ratio of Collagen I to Collagen III. Both AICAR and metformin reduced F-actin and significantly reduced the fiber cross alignment. Our results suggest that PDGFRa signaling may be an important fibrosis target and that activators of AMPK, may be an important therapeutic approach for treating CTS.

Activation of AMP-activated protein kinase by compound 991 protects osteoblasts from dexamethasone

Dexamethasone (Dex) induces direct cytotoxicity to cultured osteoblasts. The benzimidazole derivative compound 991 ("C991") is a novel and highly-efficient AMP-activated protein kinase (AMPK) activator. Here, in both MC3T3-E1 osteoblastic cells and primary murine osteoblasts, treatment with C991 activated AMPK signaling, and significantly attenuated Dex-induced apoptotic and non-apoptotic cell death. AMPKα1 knockdown (by shRNA), complete knockout (by CRISPR/Cas9 method) or dominant negative mutation (T172A) not only blocked C991-mediated AMPK activation, but also abolished its pro-survival effect against Dex in osteoblasts. Further studies showed that C991 boosted nicotinamide adenine dinucleotide phosphate (NADPH) activity and induced mRNA expression of NF-E2-related factor 2 (Nrf2)-regulated genes (heme oxygenase-1 and NADPH quinone oxidoreductase 1). Additionally, C991 alleviated Dex-induced reactive oxygen species (ROS) production in osteoblasts. Notably, genetic AMPK inhibition reversed the anti-oxidant actions by C991 in Dex-treated osteoblasts. Together, we conclude that C991 activates AMPK signaling to protect osteoblasts from Dex.

Soluble Dietary Fiber Reduces Trimethylamine Metabolism via Gut Microbiota and Co-Regulates Host AMPK Pathways

SCOPE

Evidence from animal experiments and clinical medicine suggests that high dietary fiber intake, followed by gut microbiota-mediated fermentation, decreases trimethylamine (TMA) metabolism, the mechanism of which, however, remains unclear. The objective of this analysis was to evaluate, using mice fed with red meat, the effects of soluble dietary fiber (SDF) intervention on TMA metabolism.

METHODS AND RESULTS

Low- or high-dose soluble dietary fiber (SDF) from natural wheat bran (LN and HN, low- and high-dose natural SDF), fermented wheat bran (LF and HF, low- and high-dose fermented SDF), and steam-exploded wheat bran (LE and HE, low- and high-dose exploded SDF groups) were used to examine whether SDF interventions in mice fed with red meat can alter TMA and trimethylamine N-oxide (TMAO) metabolism by gut microbial communities in a diet-specific manner. Results demonstrated that SDF-diets could reduce TMA and trimethylamine N-oxide (TMAO) metabolism by 40.6 and 62.6%, respectively. DF feeding, particularly fermented SDF, reshaped gut microbial ecology and promoted the growth of certain beneficial microflora species. SDF-diet decreased energy intake, weight gain, intestinal pH values, and serum lipid and cholesterol levels. SDF-diet also enhanced the production of short chain fatty acids with activation of the intestinal epithelial adenosine monophosphate-activated protein kinase (AMPK).

CONCLUSION

These findings suggest a central mechanism via which SDF-diet may control TMA metabolism by gut microflora and co-regulate the AMPK pathways of the host.

Respiratory stress in mitochondrial electron transport chain complex mutants of Candida albicans activates Snf1 kinase response

We have previously established that mitochondrial Complex I (CI) mutants of Candida albicans display reduced oxygen consumption, decreased ATP production, and increased reactive oxidant species (ROS) during cell growth. Using the Seahorse XF96 analyzer, the energetic phenotypes of Electron Transport Chain (ETC) complex mutants are further characterized in the current study. The underlying regulation of energetic changes in these mutants is determined in glucose and non-glucose conditions when compared to wild type (WT) cells. In parental cells, the rate of oxygen consumption remains constant for 2.5 h following the addition of glucose, oligomycin, and 2-DG, but glycolysis is highly active upon the addition of glucose. In comparison, over the same time period, electron transport complex mutants (CI, CIII and CIV) have heightened activities in both oxygen consumption and glycolysis upon glucose uptake. We refer to the response in these mutants as an "explosive respiration," which we believe is caused by low energy levels and increased production of reactive oxygen species (ROS). Accompanying this phenotype in mutants is a hyperphosphorylation of Snf1p which in Saccharomyces cerevisiae serves as an energetic stress response protein kinase for maintaining energy homeostasis. Compared to wild type cells, a 2.9- to 4.4-fold hyperphosphorylation of Snf1p is observed in all ETC mutants in the presence of glucose. However, the explosive respiration and hyperphosphorylation of Snf1 can be partially reduced by the replacement of glucose with either glycerol or oleic acid in a mutant-specific manner. Furthermore, Inhibitors of glutathione synthesis (BSO) or anti-oxidants (mito-TEMPO) likewise confirmed an increase of Sfn1 phosphorylation in WT or mutant due to increased levels of ROS. Our data establish the role of the C. albicans Snf1 as a surveyor of cell energy and ROS levels. We interpret the "explosive respiration" as a failed attempt by ETC mutants to restore energy and ROS homeostasis via Snf1 activation. An inherently high OCR baseline in WT C. albicans with a background level of Snf1 activation is a prerequisite for success in quickly fermenting glucose.

Modulating the catalytic activity of AMPK has neuroprotective effects against α-synuclein toxicity

Background

Metabolic perturbations and slower renewal of cellular components associated with aging increase the risk of Parkinson’s disease (PD). Declining activity of AMPK, a critical cellular energy sensor, may therefore contribute to neurodegeneration.

Methods

Here, we overexpress various genetic variants of the catalytic AMPKα subunit to determine how AMPK activity affects the survival and function of neurons overexpressing human α-synuclein in vivo.

Results

Both AMPKα1 and α2 subunits have neuroprotective effects against human α-synuclein toxicity in nigral dopaminergic neurons. Remarkably, a modified variant of AMPKα1 (T172Dα1) with constitutive low activity most effectively prevents the loss of dopamine neurons, as well as the motor impairments caused by α-synuclein accumulation. In the striatum, T172Dα1 decreases the formation of dystrophic axons, which contain aggregated α-synuclein. In primary cortical neurons, overexpression of human α-synuclein perturbs mitochondrial and lysosomal activities. Co-expressing AMPKα with α-synuclein induces compensatory changes, which limit the accumulation of lysosomal material and increase the mitochondrial mass.

Conclusions

Together, these results indicate that modulating AMPK activity can mitigate α-synuclein toxicity in nigral dopamine neurons, which may have implications for the development of neuroprotective treatments against PD.

Electronic supplementary material

The online version of this article (10.1186/s13024-017-0220-x) contains supplementary material, which is available to authorized users.

CDK4 Phosphorylates AMPKα2 to Inhibit Its Activity and Repress Fatty Acid Oxidation

The roles of CDK4 in the cell cycle have been extensively studied, but less is known about the mechanisms underlying the metabolic regulation by CDK4. Here, we report that CDK4 promotes anaerobic glycolysis and represses fatty acid oxidation in mouse embryonic fibroblasts (MEFs) by targeting the AMP-activated protein kinase (AMPK). We also show that fatty acid oxidation (FAO) is specifically induced by AMPK complexes containing the α2 subunit. Moreover, we report that CDK4 represses FAO through direct phosphorylation and inhibition of AMPKα2. The expression of non-phosphorylatable AMPKα2 mutants, or the use of a CDK4 inhibitor, increased FAO rates in MEFs and myotubes. In addition, Cdk4-/- mice have increased oxidative metabolism and exercise capacity. Inhibition of CDK4 mimicked these alterations in normal mice, but not when skeletal muscle was AMPK deficient. This novel mechanism explains how CDK4 promotes anabolism by blocking catabolic processes (FAO) that are activated by AMPK.

Hydrogen Sulphide Treatment Increases Insulin Sensitivity and Improves Oxidant Metabolism through the CaMKKbeta-AMPK Pathway in PA-Induced IR C2C12 Cells

Studies have reported attenuation of insulin resistance (IR) by improving phosphorylation of the insulin signalling pathway. However, the upstream molecular signalling pathway is still elusive. In this study, Western blot was used to evaluate the phosphorylation level of the insulin signalling pathway and the AMPK pathway. 2-NBDG was used to evaluate glucose uptake. Ca²⁺ imaging was used to assess change of intracellular Ca²⁺ concentration. We found that NaHS enhanced the intracellular Ca²⁺ concentration and glucose uptake and activated the insulin signalling cascade in a palmitic acid (PA)-induced IR model in C2C12 cells. Furthermore, activation of the IRS1/PI3K/AKT pathway and glucose uptake were decreased when AMPK or CaMKKβ was inhibited. Our study also showed that the mitochondrial electron transport chain, ATP production, and intramitochondrial cAMP declined in the IR model but that this effect was reversed by NaHS, an effect that may be mediated by the Ca²⁺/CaMKK2/AMPK and PI3K/AKT pathways. Our data indicate that H₂S improves activation of the insulin signalling cascade and glucose uptake via activation of the Ca²⁺/CaMKK2/AMPK pathway and mitochondrial metabolism in C2C12 cells. Furthermore, NaHS protects mitochondrial function and maintains normal ATP production by activating the cAMP system and the Ca²⁺/CaMKK2/AMPK and PI3K/ATK pathways.

Decaffeinated green and black tea polyphenols decrease weight gain and alter microbiome populations and function in diet-induced obese mice

PURPOSE

Decaffeinated green tea (GT) and black tea (BT) polyphenols inhibit weight gain in mice fed an obesogenic diet. Since the intestinal microflora is an important contributor to obesity, it was the objective of this study to determine whether the intestinal microflora plays a role in the anti-obesogenic effect of GT and BT.

METHODS

C57BL/6J mice were fed a high-fat/high-sucrose diet (HF/HS, 32% energy from fat; 25% energy from sucrose) or the same diet supplemented with 0.25% GTP or BTP or a low-fat/high-sucrose (LF/HS, 10.6% energy from fat, 25% energy from sucrose) diet for 4 weeks. Bacterial composition was assessed by MiSeq sequencing of the 16S rRNA gene.

RESULTS

GTP and BTP diets resulted in a decrease of cecum Firmicutes and increase in Bacteroidetes. The relative proportions of Blautia, Bryantella, Collinsella, Lactobacillus, Marvinbryantia, Turicibacter, Barnesiella, and Parabacteroides were significantly correlated with weight loss induced by tea extracts. BTP increased the relative proportion of Pseudobutyrivibrio and intestinal formation of short-chain fatty acids (SCFA) analyzed by gas chromatography. Cecum propionic acid content was significantly correlated with the relative proportion of Pseudobutyrivibrio. GTP and BTP induced a significant increase in hepatic 5'adenosylmonophosphate-activated protein kinase (AMPK) phosphorylation by 70 and 289%, respectively (P < 0.05) determined by Western blot.

CONCLUSION

In summary, both BTP and GTP induced weight loss in association with alteration of the microbiota and increased hepatic AMPK phosphorylation. We hypothesize that BTP increased pAMPK through increased intestinal SCFA production, while GTPs increased hepatic AMPK through GTP present in the liver.

The autophagy initiator ULK1 sensitizes AMPK to allosteric drugs

AMP-activated protein kinase (AMPK) is a metabolic stress-sensing enzyme responsible for maintaining cellular energy homeostasis. Activation of AMPK by salicylate and the thienopyridone A-769662 is critically dependent on phosphorylation of Ser108 in the β1 regulatory subunit. Here, we show a possible role for Ser108 phosphorylation in cell cycle regulation and promotion of pro-survival pathways in response to energy stress. We identify the autophagy initiator Unc-51-like kinase 1 (ULK1) as a β1-Ser108 kinase in cells. Cellular β1-Ser108 phosphorylation by ULK1 was dependent on AMPK β-subunit myristoylation, metabolic stress associated with elevated AMP/ATP ratio, and the intrinsic energy sensing capacity of AMPK; features consistent with an AMP-induced myristoyl switch mechanism. We further demonstrate cellular AMPK signaling independent of activation loop Thr172 phosphorylation, providing potential insight into physiological roles for Ser108 phosphorylation. These findings uncover new mechanisms by which AMPK could potentially maintain cellular energy homeostasis independently of Thr172 phosphorylation.

AMPK is involved in sensing of metabolic stress. The authors show that the autophagy initiator ULK1 phosphorylates β1-Ser108 on the regulatory β1-subunit, sensitizing AMPK to allosteric drugs, and activates signaling pathways that appear independent of Thr172 phosphorylation in the kinase activation loop.

AICAR Administration Attenuates Hemorrhagic Hyperglycemia and Lowers Oxygen Debt in Anesthetized Male Rabbits

Background: Many strategies have been utilized to treat traumatic shock via improved oxygen delivery (DO₂), while fewer have been used to in an attempt to reduce oxygen demand (VO₂). The cellular energy sensor 5′ adenosine monophosphate-activated protein kinase (AMPK) has the potential to modulate both whole-body DO₂ and VO₂. Therefore, we determined the effect of the AMPK activator AICAR (5-aminoimidazole-4-carboxamide 1-β-D-ribonucleoside) given acutely or chronically on key metabolites, hemodynamics, and oxygen consumption/delivery before and during hemorrhage in anesthetized male rabbits.

Methods: Chronically treated animals received AICAR (40 mg/kg/day, IV) for 10 days prior to hemorrhage, while rabbits in the acute study were infused with AICAR (7.5 mg/kg bolus, 2 mg/kg/min infusion) or vehicle (0.3 ml/kg saline bolus, 0.03 ml/kg/min infusion) IV for 2 h prior to severe hemorrhage. Both acutely and chronically treated animals were sedated (ketamine/xylazine cocktail) the morning of the terminal experiment and surgically prepared for hemorrhage, including the implantation of arterial and venous catheters (for blood removal/sampling and drug/vehicle administration) and thoracotomy for implantation of transit-time flow transducers (for cardiac output determination).

Results: AICAR given acutely lowered arterial blood glucose and increased blood lactate levels before hemorrhage, and abolished the well-documented hemorrhage-induced hyperglycemia seen in vehicle treated animals. Animals given AICAR chronically had blunted hemorrhage-induced hyperglycemia without prior baseline changes. Chronically treated AICAR animals showed significantly lower lactate levels during hemorrhage. Rabbits receiving AICAR both acutely and chronically experienced similar falls in mean arterial pressure, cardiac output and hence DO₂ to their vehicle counterparts throughout the hemorrhage period. However, rabbits treated either acutely or chronically with AICAR accumulated lower oxygen deficits and debt during hemorrhage compared to vehicle-infused controls.

Conclusions: The oxygen debt data suggest that AMPK activation could decrease trauma associated morbidity and mortality, perhaps by mechanisms related to increased glucose utilization. Additional studies are needed to investigate the effects of AICAR and associated mechanisms of action when given during resuscitation from hemorrhage.

AMPK activation: Role in the signaling pathways of neuroinflammation and neurodegeneration

Adenosine monophosphate-activated protein kinase (AMPK) is an evolutionarily conserved sensor of cellular energy status and has been reported to be involved in chronic inflammatory disorders. AMPK is expressed in immune cells, such as dendritic cells, macrophages, lymphocytes and neutrophils, and is an important regulator of inflammatory responses through the regulation of complex signaling networks in part by inhibiting downstream cascade pathways, such as nuclear factor kB, which is a key regulator of innate immunity and inflammation, as well as acting as a negative regulator of toll-like receptors. Recent data suggest that AMPK dysregulation may participate in neurodegenerative diseases, such as multiple sclerosis, Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and neuropathies. However, there are conflicting reports on the benefits or detrimental effects of AMPK in distinct pathological conditions. This paper offers a review of the recent literature on the pharmacological modulation of the AMPK system as a potential molecular target in the management of neurodegenerative diseases.

Aging: Molecular Pathways and Implications on the Cardiovascular System

The world's population over 60 years is growing rapidly, reaching 22% of the global population in the next decades. Despite the increase in global longevity, individual healthspan needs to follow this growth. Several diseases have their prevalence increased by age, such as cardiovascular diseases, the leading cause of morbidity and mortality worldwide. Understanding the aging biology mechanisms is fundamental to the pursuit of cardiovascular health. In this way, aging is characterized by a gradual decline in physiological functions, involving the increased number in senescent cells into the body. Several pathways lead to senescence, including oxidative stress and persistent inflammation, as well as energy failure such as mitochondrial dysfunction and deregulated autophagy, being ROS, AMPK, SIRTs, mTOR, IGF-1, and p53 key regulators of the metabolic control, connecting aging to the pathways which drive towards diseases. In addition, senescence can be induced by cellular replication, which resulted from telomere shortening. Taken together, it is possible to draw a common pathway unifying aging to cardiovascular diseases, and the central point of this process, senescence, can be the target for new therapies, which may result in the healthspan matching the lifespan.

Diet-induced modifications to milk composition have long-term effects on offspring growth in rabbits

It has been clearly demonstrated that the maternal nutritional status during pregnancy and lactation has long-term effects on offspring health. In mammals, milk represents the first maternal support provided to the newborns so that its composition may play a major role in long-term programming. We therefore assessed the effects of maternal high-fat/high-sugar obesogenic (OD) or control (CD) diets on offspring growth and adiposity in the rabbit. Between 7 and 20 wk of age, the BW gain of OD milk-fed rabbits was higher than that of CD milk-fed rabbits ( < 0.05). Body fat mass measurements at 21 wk of age revealed a significant increase in body adiposity as a function of milk ingested during the neonatal period, in both female and male offspring ( < 0.05). A marked weight gain difference was observed according to the milk in both female and male offspring. Moreover, we investigated the composition in major proteins and leptin levels in milk from OD or CD diet-fed dams. Liquid chromatography-mass spectrometry analysis of individual CD skimmed milk samples enabled identification and quantification of the rabbit main milk proteins and of their main phosphorylated isoforms at 2 different stages of lactation (3 and 10 d). Here we show that the OD diet induced a reduction in the whey acidic protein content concomitantly with both an increase in serum albumin and lactoferrin contents and in the phosphorylated isoforms of the main milk proteins. Furthermore, a sharp rise in leptin levels was observed in the milk of OD diet-fed dams on Day 10 of lactation when compared with CD diet animals ( < 0.05). Taken together, these findings provide evidence that lactation is a critical window of development during which exposure to a deleterious diet is highly detrimental to long-term outcomes. Moreover, these insights suggest that it may be possible to prevent at least some of the adverse effects of inadequate maternal nutrition on the long-term metabolic outcomes of the offspring through nutritional interventions applied during the lactation period.

Pharmacological activation of AMPK inhibits incision-evoked mechanical hypersensitivity and the development of hyperalgesic priming in mice

New therapeutics to manage post-surgical pain are needed to mitigate the liabilities of opioid and other analgesics. Our previous work shows that key modulators of excitability in peripheral nociceptors, such as extracellular signal-regulated kinases (ERK) are inhibited by activation of adenosine monophosphate activated protein kinase (AMPK). We hypothesized that AMPK activation would attenuate acute incision-evoked mechanical hypersensitivity and the development of hyperalgesic priming caused by surgery in mice. Here we have used a variety of administration routes and combinations of AMPK activators to test this hypothesis. Topical administration of a resveratrol-based cream inhibited acute mechanical hypersensitivity evoked by incision and blocked the development of hyperalgesic priming. We also observed that systemic administration of metformin dose-dependently inhibited incision-evoked mechanical hypersensitivity and hyperalgesic priming. Interestingly, low doses of systemic metformin and local resveratrol that had no acute effect were able to mitigate development of hyperalgesic priming. Combined treatment with doses of systemic metformin and local resveratrol that were not effective on their own enhanced the acute efficacy of the individual AMPK activators for post-surgical mechanical pain alleviation and blocked the development of hyperalgesic priming. Finally, we used dorsal root ganglion (DRG) neurons in culture to show that resveratrol and metformin given in combination shift the concentration-response curve for AMPK activation to the left and increase the magnitude of AMPK activation. Therefore, we find that topical administration is an effective treatment route of administration and combining systemic and local treatments led to anti-nociceptive efficacy in acute mechanical hypersensitivity at doses that were not effective alone. Collectively our work demonstrates a specific effect of AMPK activators on post-surgical pain and points to novel therapeutic opportunities with potential immediate impact in the clinical setting.

Molecular mechanisms of appetite and obesity: a role for brain AMPK

Feeding behaviour and energy storage are both crucial aspects of survival. Thus, it is of fundamental importance to understand the molecular mechanisms regulating these basic processes. The AMP-activated protein kinase (AMPK) has been revealed as one of the key molecules modulating energy homoeostasis. Indeed, AMPK appears to be essential for translating nutritional and energy requirements into generation of an adequate neuronal response, particularly in two areas of the brain, the hypothalamus and the hindbrain. Failure of this physiological response can lead to energy imbalance, ultimately with extreme consequences, such as leanness or obesity. Here, we will review the data that put brain AMPK in the spotlight as a regulator of appetite.

Energy balance, body composition, sedentariness and appetite regulation: pathways to obesity

Energy balance is not a simple algebraic sum of energy expenditure and energy intake as often depicted in communications. Energy balance is a dynamic process and there exist reciprocal effects between food intake and energy expenditure. An important distinction is that of metabolic and behavioural components of energy expenditure. These components not only contribute to the energy budget directly, but also by influencing the energy intake side of the equation. It has recently been demonstrated that resting metabolic rate (RMR) is a potential driver of energy intake, and evidence is accumulating on the influence of physical activity (behavioural energy expenditure) on mechanisms of satiety and appetite control. These effects are associated with changes in leptin and insulin sensitivity, and in the plasma levels of gastrointestinal (GI) peptides such as glucagon-like peptide-1 (GLP-1), ghrelin and cholecystokinin (CCK). The influence of fat-free mass on energy expenditure and as a driver of energy intake directs attention to molecules emanating from skeletal tissue as potential appetite signals. Sedentariness (physical inactivity) is positively associated with adiposity and is proposed to be a source of overconsumption and appetite dysregulation. The molecular signals underlying these effects are not known but represent a target for research.

The metabolic sensor AKIN10 modulates the Arabidopsis circadian clock in a light-dependent manner

Plants generate rhythmic metabolism during the repetitive day/night cycle. The circadian clock produces internal biological rhythms to synchronize numerous metabolic processes such that they occur at the required time of day. Metabolism conversely influences clock function by controlling circadian period and phase and the expression of core-clock genes. Here, we show that AKIN10, a catalytic subunit of the evolutionarily conserved key energy sensor sucrose non-fermenting 1 (Snf1)-related kinase 1 (SnRK1) complex, plays an important role in the circadian clock. Elevated AKIN10 expression led to delayed peak expression of the circadian clock evening-element GIGANTEA (GI) under diurnal conditions. Moreover, it lengthened clock period specifically under light conditions. Genetic analysis showed that the clock regulator TIME FOR COFFEE (TIC) is required for this effect of AKIN10. Taken together, we propose that AKIN10 conditionally works in a circadian clock input pathway to the circadian oscillator.

Unravelling the complexity of signalling networks in cancer: A review of the increasing role for computational modelling

Cancer induction is a highly complex process involving hundreds of different inducers but whose eventual outcome is the same. Clearly, it is essential to understand how signalling pathways and networks generated by these inducers interact to regulate cell behaviour and create the cancer phenotype. While enormous strides have been made in identifying key networking profiles, the amount of data generated far exceeds our ability to understand how it all "fits together". The number of potential interactions is astronomically large and requires novel approaches and extreme computation methods to dissect them out. However, such methodologies have high intrinsic mathematical and conceptual content which is difficult to follow. This review explains how computation modelling is progressively finding solutions and also revealing unexpected and unpredictable nano-scale molecular behaviours extremely relevant to how signalling and networking are coherently integrated. It is divided into linked sections illustrated by numerous figures from the literature describing different approaches and offering visual portrayals of networking and major conceptual advances in the field. First, the problem of signalling complexity and data collection is illustrated for only a small selection of known oncogenes. Next, new concepts from biophysics, molecular behaviours, kinetics, organisation at the nano level and predictive models are presented. These areas include: visual representations of networking, Energy Landscapes and energy transfer/dissemination (entropy); diffusion, percolation; molecular crowding; protein allostery; quinary structure and fractal distributions; energy management, metabolism and re-examination of the Warburg effect. The importance of unravelling complex network interactions is then illustrated for some widely-used drugs in cancer therapy whose interactions are very extensive. Finally, use of computational modelling to develop micro- and nano- functional models ("bottom-up" research) is highlighted. The review concludes that computational modelling is an essential part of cancer research and is vital to understanding network formation and molecular behaviours that are associated with it. Its role is increasingly essential because it is unravelling the huge complexity of cancer induction otherwise unattainable by any other approach.

Heterologous production of a ginsenoside saponin (compound K) and its precursors in transgenic tobacco impairs the vegetative and reproductive growth

MAIN CONCLUSION

Production of compound K (a ginsenoside saponin) and its precursors in transgenic tobacco resulted in stunted growth and seed set failure, which may be caused by strong autotoxicity of heterologously produced phytochemicals against the tobacco itself. Panax ginseng roots contain various saponins (ginsenosides), which are major bioactive compounds. A monoglucosylated saponin, compound K (20-O-(β-D-glucopyranosyl)-20(S)-protopanaxadiol), has high medicinal and cosmetic values but is present in undetectable amounts in naturally grown ginseng roots. The production of compound K (CK) requires complicated deglycosylation of ginsenosides using physicochemical and/or enzymatic degradation. In this work, we report the production of CK in transgenic tobacco by co-overexpressing three genes (PgDDS, CYP716A47 and UGT71A28) isolated from P. ginseng. Introduction and expression of the transgenes in tobacco lines were confirmed by genomic PCR and RT-PCR. All the lines of transgenic tobacco produced CK including its precursors, protopanaxadiol and dammarenediol-II (DD). The concentrations of CK in the leaves ranged from 1.55 to 2.64 µg/g dry weight, depending on the transgenic line. Interestingly, production of CK in tobacco brought stunted plant growth and gave rise to seed set failure. This seed set failure was caused by both long-styled flowers and abnormal pollen development in transgenic tobacco. Both CK and DD treatments highly suppressed in vitro germination and tube growth in wild-type pollens. Based on these results, metabolic engineering for CK production in transgenic tobacco was successfully achieved, but the production of CK and its precursors in tobacco severely affects vegetative and reproductive growth due to the cytotoxicity of phytochemicals that are heterologously produced in transgenic tobacco.

A novel PRKAG2 mutation in a Chinese family with cardiac hypertrophy and ventricular pre-excitation

PRKAG2 syndrome is a rare autosomal dominant inherited disorder that is characterized by cardiac hypertrophy, ventricular pre-excitation and conduction system abnormalities. There is little knowledge in cardiovascular magnetic resonance (CMR) characteristics of PRKAG2 cardiomyopathy. This study investigated the genetic defect in a three-generation Chinese family with cardiac hypertrophy and ventricular pre-excitation using whole-exome sequencing. A novel missense mutation, c.1006 G > T (p.V336L), was identified in PRKAG2. This mutation had not been identified in the ExAC database, and the prediction result of MutationTaster indicated a deleterious effect. Furthermore, it cosegregated with the disease in the present family and was absent in unrelated 300 healthy controls. cDNA analysis did not detect any splicing defects, although the variant occurred in the first base of exon 9. CMR evaluation in five affected members showed diffuse hypertrophy in a concentric pattern, with markedly increased left ventricular mass above age and gender limits (median 151.3 g/m², range 108.4–233.4 g/m²). Two patients in progressive stage and one patient with sudden cardiac death exhibited extensive subendocardial late gadolinium enhancement. In conclusion, molecular screening for PRKAG2 mutations should be considered in patients who exhibit cardiac hypertrophy coexisting with ventricular pre-excitation. CMR offers promising advantages for evaluation of PRKAG2 cardiomyopathy.

Aldehyde dehydrogenase-2 (ALDH2) opposes hepatocellular carcinoma progression by regulating AMP-activated protein kinase signaling in mice

Potential biomarkers that can be used to determine prognosis and perform targeted therapies are urgently needed to treat patients with hepatocellular carcinoma (HCC). To meet this need, we performed a screen to identify functional genes associated with hepatocellular carcinogenesis and its progression at the transcriptome and proteome levels. We identified aldehyde dedydrogenase-2 (ALDH2) as a gene of interest for further study. ALDH2 levels were significantly lower at the mRNA and protein level in tumor tissues than in normal tissues, and they were even lower in tissues that exhibited increased migratory capacity. A study of clinical associations showed that ALDH2 is correlated with survival and multiple migration-associated clinicopathological traits, including the presence of metastasis and portal vein tumor thrombus. The result of overexpressing or knocking down ALDH2 showed that this gene inhibited migration and invasion both in vivo and in vitro. We also found that ALDH2 altered the redox status of cells by regulating acetaldehyde levels and that it further activated the AMP-activated protein kinase (AMPK) signaling pathway.

CONCLUSION

Decreased levels of ALDH2 may indicate a poor prognosis in HCC patients, while forcing the expression of ALDH2 in HCC cells inhibited their aggressive behavior in vitro and in mice largely by modulating the activity of the ALDH2-acetaldehyde-redox-AMPK axis. Therefore, identifying ALDH2 expression levels in HCC might be a useful strategy for classifying HCC patients and for developing potential therapeutic strategies that specifically target metastatic HCC. (Hepatology 2017;65:1628-1644).

Regulation of organelle function by metformin

Metformin ameliorates hyperglycemia without the side effects of lactic acidosis or hypoglycemia. Metformin lowers the blood glucose level by decreasing hepatic glucose production in the liver and by increasing glucose uptake in the muscle. Recent studies show that metformin induces cell death in certain cancer cell lines by interfering with the metabolism of the cancer cells. Therefore, understanding the mechanisms of action for metformin will provide insights into how to better treat diabetes and other metabolic disorders and also into the development of new therapeutic drugs. One of the best understood molecular targets of metformin is the mitochondrial complex I. However, given metformin's broad effects on metabolism, it could act on multiple targets. In this review, we summarize current findings in metformin's mechanisms of action regarding its known targets in mitochondria and known effects in cancer cell lines. Then, we introduce endosomal Na⁺ /H⁺ exchangers and the V-ATPase as new potential targets of metformin's action. Finally, we will discuss the hypothesis that metformin directly acts on endosome/lysosome regulation so as to regulate metabolism and ultimately alleviate type 2 diabetes. © 2017 IUBMB Life, 69(7):459-469, 2017.

ROS signaling under metabolic stress: cross-talk between AMPK and AKT pathway

Cancer cells are frequently confronted with metabolic stress in tumor microenvironments due to their rapid growth and limited nutrient supply. Metabolic stress induces cell death through ROS-induced apoptosis. However, cancer cells can adapt to it by altering the metabolic pathways. AMPK and AKT are two primary effectors in response to metabolic stress: AMPK acts as an energy-sensing factor which rewires metabolism and maintains redox balance. AKT broadly promotes energy production in the nutrient abundance milieu, but the role of AKT under metabolic stress is in dispute. Recent studies show that AMPK and AKT display antagonistic roles under metabolic stress. Metabolic stress-induced ROS signaling lies in the hub between metabolic reprogramming and redox homeostasis. Here, we highlight the cross-talk between AMPK and AKT and their regulation on ROS production and elimination, which summarizes the mechanism of cancer cell adaptability under ROS stress and suggests potential options for cancer therapeutics.

ROS signaling under metabolic stress: cross-talk between AMPK and AKT pathway

Cancer cells are frequently confronted with metabolic stress in tumor microenvironments due to their rapid growth and limited nutrient supply. Metabolic stress induces cell death through ROS-induced apoptosis. However, cancer cells can adapt to it by altering the metabolic pathways. AMPK and AKT are two primary effectors in response to metabolic stress: AMPK acts as an energy-sensing factor which rewires metabolism and maintains redox balance. AKT broadly promotes energy production in the nutrient abundance milieu, but the role of AKT under metabolic stress is in dispute. Recent studies show that AMPK and AKT display antagonistic roles under metabolic stress. Metabolic stress-induced ROS signaling lies in the hub between metabolic reprogramming and redox homeostasis. Here, we highlight the cross-talk between AMPK and AKT and their regulation on ROS production and elimination, which summarizes the mechanism of cancer cell adaptability under ROS stress and suggests potential options for cancer therapeutics.

Mitochondrial Reactive Oxygen Species and Kidney Hypoxia in the Development of Diabetic Nephropathy

The underlying mechanisms in the development of diabetic nephropathy are currently unclear and likely consist of a series of dynamic events from the early to late stages of the disease. Diabetic nephropathy is currently without curative treatments and it is acknowledged that even the earliest clinical manifestation of nephropathy is preceded by an established morphological renal injury that is in turn preceded by functional and metabolic alterations. An early manifestation of the diabetic kidney is the development of kidney hypoxia that has been acknowledged as a common pathway to nephropathy. There have been reports of altered mitochondrial function in the diabetic kidney such as altered mitophagy, mitochondrial dynamics, uncoupling, and cellular signaling through hypoxia inducible factors and AMP-kinase. These factors are also likely to be intertwined in a complex manner. In this review, we discuss how these pathways are connected to mitochondrial production of reactive oxygen species (ROS) and how they may relate to the development of kidney hypoxia in diabetic nephropathy. From available literature, it is evident that early correction and/or prevention of mitochondrial dysfunction may be pivotal in the prevention and treatment of diabetic nephropathy.

Geniposide protects pancreatic β cells from high glucose-mediated injury by activation of AMP-activated protein kinase

Our previous works indicated that geniposide could regulate glucose-stimulated insulin secretion (GSIS), and improved chronic high glucose-induced dysfunctions in pancreatic β cells, but the molecular mechanisms remain largely unknown. In the present study, we investigated the role of 5'-AMP-activated protein kinase (AMPK) in high glucose induced cell injury and explored the associated molecular mechanisms in rat INS-1 pancreatic β cells. Data suggested that geniposide obviously prevented the cell damage induced by high (25 mM) glucose in INS-1 cells, which increased the protein levels of cell apoptosis-associated enzymes, including heme oxygenase-1 (HO-1), and Bcl-2, but apparently attenuated the protein level of Bax, an apoptotic protein. In addition, Compound C, an AMPK inhibitor, remarkably inhibited the effects of geniposide on the protein levels of HO-1, Bcl-2, and Bax, but AICAR, an AMPK activator, potentiated the role of geniposide on the protein levels of HO-1, Bcl-2, and Bax. More importantly, geniposide directly prevented the cleavage of caspase-3 induced by high glucose, and this effect was also evidently prohibited by the pre-incubation of compound C in high glucose-treated INS-1 cells. Furthermore, using the method of RNA interfere, we further proved that treatment with AMPK siRNA attenuated the effects of geniposide on the apoptosis-associated proteins and cell viability. All these data suggest that AMPK plays a crucial role on geniposide antagonizing high glucose-induced pancreatic β cells injury.

Targeting the energy guardian AMPK: another avenue for treating cardiomyopathy?

5'-AMP-activated protein kinase (AMPK) is a pivotal regulator of endogenous defensive molecules in various pathological processes. The AMPK signaling regulates a variety of intracellular intermedial molecules involved in biological reactions, including glycogen metabolism, protein synthesis, and cardiac fibrosis, in response to hypertrophic stimuli. Studies have revealed that the activation of AMPK performs a protective role in cardiovascular diseases, whereas its function in cardiac hypertrophy and cardiomyopathy remains elusive and poorly understood. In view of the current evidence of AMPK, we introduce the biological information of AMPK and cardiac hypertrophy as well as some upstream activators of AMPK. Next, we discuss two important types of cardiomyopathy involving AMPK, RKAG2 cardiomyopathy, and hypertrophic cardiomyopathy. Eventually, therapeutic research, genetic screening, conflicts, obstacles, challenges, and potential directions are also highlighted in this review, aimed at providing a comprehensive understanding of AMPK for readers.

Metformin-like antidiabetic, cardio-protective and non-glycemic effects of naringenin: Molecular and pharmacological insights

Metformin is a widely used drug for the treatment of type 2 diabetes (T2D). Its blood glucose-lowering effects are initially due to inhibition of hepatic glucose production and increased peripheral glucose utilization. Metformin has also been shown to have several beneficial effects on cardiovascular risk factors and it is the only oral antihyperglycaemic agent thus far associated with decreased macrovascular complications in patients with diabetes. Adenosine Monophosphate Activated-Protein Kinase (AMPK) is a major cellular regulator of lipid and glucose metabolism. Recent evidence shows that pharmacological activation of AMPK improves blood glucose homeostasis, lipid profiles, blood pressure and insulin-resistance making it a novel therapeutic target in the treatment of T2D. Naringenin a flavonoid found in high concentrations as its glycone naringin in citrus fruits, has been reported to have antioxidant, antiatherogenic, anti- dyslipidemic and anti-diabetic effects. It has been shown that naringenin exerts its anti-diabetic effects by inhibition of gluconeogenesis through upregulations of AMPK hence metformin-like effects. Naringin has further been shown to have non-glycemic affects like metformin that mitigate inflammation and cell proliferation. This review evaluates the potential of naringenin as anti-diabetic, anti-dyslipidemic anti-inflammatory and antineoplastic agent similar to metformin and proposes its further development for therapeutic use in clinical practice.