Inhibition Of Adenosine Monophosphate-activated Kinase Research Articles

Pathogenesis of Alcoholic Fatty Liver a Narrative Review.

Alcohol effect hepatic lipid metabolism through various mechanisms, leading synergistically to an accumulation of fatty acids (FA) and triglycerides. Obesity, as well as dietary fat (saturated fatty acids (FA) versus poly-unsaturated fatty acids (PUFA)) may modulate the hepatic fat. Alcohol inhibits adenosine monophosphate activated kinase (AMPK). AMPK activates peroxisome proliferator activated receptor a (PPARα) and leads to a decreased activation of sterol regulatory element binding protein 1c (SRABP1c). The inhibition of AMPK, and thus of PPARα, results in an inhibition of FA oxidation. This ß-oxidation is further reduced due to mitochondrial damage induced through cytochrome P4502E1 (CYP2E1)-driven oxidative stress. Furthermore, the synthesis of FAs is stimulated through an activation of SHREP1. In addition, alcohol consumption leads to a reduced production of adiponectin in adipocytes due to oxidative stress and to an increased mobilization of FAs from adipose tissue and from the gut as chylomicrons. On the other side, the secretion of FAs via very-low-density lipoproteins (VLDL) from the liver is inhibited by alcohol. Alcohol also affects signal pathways such as early growth response 1 (Egr-1) associated with the expression of tumour necrosis factor α (TNF α), and the mammalian target of rapamycin (mTOR) a key regulator of autophagy. Both have influence the pathogenesis of alcoholic fatty liver. Alcohol-induced gut dysbiosis contributes to the severity of ALD by increasing the metabolism of ethanol in the gut and promoting intestinal dysfunction. Moreover, pathogen-associated molecular patterns (PAMPS) via specific Toll-like receptor (TLR) bacterial overgrowth leads to the translocation of bacteria. Endotoxins and toxic ethanol metabolites enter the enterohepatic circulation, reaching the liver and inducing the activation of the nuclear factor kappa-B (NFκB) pathway. Pro-inflammatory cytokines released in the process contribute to inflammation and fibrosis. In addition, cellular apoptosis is inhibited in favour of necrosis.

SIRT1-dependent AMPK pathway in the protection of estrogen against ischemic brain injury.

Stroke is a major cause of mortality and disability, especially for postmenopausal women. In view of the protective action of estrogen, hormone therapy remains the only effective way to limit this risk. The objective of this study was to investigate the efficiency and underlying mechanisms of estrogen neuroprotection. Subcutaneous injection of 17β-estradiol in rats after ovariectomy (OVX) was used to manipulate estrogen level and explore the effects of estrogen in cerebral ischemic damage both in vivo and in vitro. Silent mating type information regulation 2 homolog 1 (SIRT1) knockout mice and adenosine monophosphate (AMP)-activated kinase (AMPK) inhibitor Compound C were also used to investigate the underlying pathway of estrogen. Estrogen deficiency induced by OVX aggravated brain infarction in experimentally induced cerebral ischemia rats, whereas estrogen pretreatment reduced ischemia-induced cerebral injuries. Neurons of estrogen deficiency models were susceptible to apoptosis under oxygen-glucose deprivation (OGD). In contrast, neurons with estrogen-supplemented serum exhibited restored resistance to cell apoptosis. In OGD neurons, estrogen promoted AMPK activation through estrogen receptor α, and neuroprotection of estrogen was prevented by AMPK inhibition. Estrogen increased SIRT1 expression and activation, and estrogen-induced AMPK activation disappeared in SIRT1 knockout neurons. Moreover, estrogen-induced neuroprotection was abolished in SIRT1 knockout mice and AMPK-inhibited rats. Our data support that estrogen protects against ischemic stroke through preventing neuron death via the SIRT1-dependent AMPK pathway.

Re-sensitization of radiation resistant colorectal cancer cells to radiation through inhibition of AMPK pathway.

Radiotherapy (RT) is commonly used to treat multi-tumors to attenuate the risk of recurrence. Despite impressive initial clinical responses, a large proportion of patients experience resistance to RT. Therefore, identification of functionally relevant biomarkers would be beneficial for radioresistant patients. Adenosine monophosphate-activated kinase (AMPK) is recognized as a mediator of tumor suppressor gene function. In the present study, radio-sensitive and -resistant colon cancer patient samples were compared and the AMPK pathway was observed to be highly activated in radioresistant patients. In addition, the protein and mRNA levels of AMPK were upregulated in radioresistant colon cancer cells in comparison to radiosensitive colon cancer cells. The present study provides evidence that activation of AMPK by metformin contributes to radioresistance. Inhibition of AMPK by either small interfering RNA or Compound C, which is a specific inhibitor of AMPK, re-sensitized radiation resistant cells. The data presented indicates a synergistic effect on radiation resistant cancer cells by the combination of Compound C and radiation. In summary, the present study proposes that inhibition of the AMPK pathway is a potential strategy for reversing radiation resistance and may contribute to the development of therapeutic anticancer drugs.

Sphingosine-1-Phosphate Is a Novel Regulator of Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Activity.

The cystic fibrosis transmembrane conductance regulator (CFTR) attenuates sphingosine-1-phosphate (S1P) signaling in resistance arteries and has emerged as a prominent regulator of myogenic vasoconstriction. This investigation demonstrates that S1P inhibits CFTR activity via adenosine monophosphate-activated kinase (AMPK), establishing a potential feedback link. In Baby Hamster Kidney (BHK) cells expressing wild-type human CFTR, S1P (1μmol/L) attenuates forskolin-stimulated, CFTR-dependent iodide efflux. S1P’s inhibitory effect is rapid (within 30 seconds), transient and correlates with CFTR serine residue 737 (S737) phosphorylation. Both S1P receptor antagonism (4μmol/L VPC 23019) and AMPK inhibition (80μmol/L Compound C or AMPK siRNA) attenuate S1P-stimluated (i) AMPK phosphorylation, (ii) CFTR S737 phosphorylation and (iii) CFTR activity inhibition. In BHK cells expressing the ΔF508 CFTR mutant (CFTRΔF508), the most common mutation causing cystic fibrosis, both S1P receptor antagonism and AMPK inhibition enhance CFTR activity, without instigating discernable correction. In summary, we demonstrate that S1P/AMPK signaling transiently attenuates CFTR activity. Since our previous work positions CFTR as a negative S1P signaling regulator, this signaling link may positively reinforce S1P signals. This discovery has clinical ramifications for the treatment of disease states associated with enhanced S1P signaling and/or deficient CFTR activity (e.g. cystic fibrosis, heart failure). S1P receptor/AMPK inhibition could synergistically enhance the efficacy of therapeutic strategies aiming to correct aberrant CFTR trafficking.

Chronological changes and effects of AMP-activated kinase in the hippocampal CA1 region after transient forebrain ischemia in gerbils

Objectives: Adenosine monophosphate-activated kinase (AMPK) is an energy-specific sensor within the central nervous system. In this study, we observed AMPK and its phosphorylated form (pAMPK) in the hippocampal CA1 region after 5 minutes of transient forebrain ischemia. In addition, we also investigated the effects of Compound C, an AMPK inhibitor, against ischemic damage in gerbils.Methods: Adenosine monophosphate-activated kinase and pAMPK immunoreactivity was observed in the hippocampal CA1 region at various time points after ischemia and Compound C was intraperitoneally administered to gerbils immediately after reperfusion and the animals were sacrificed at 5 days after ischemia/reperfusion.Results: Adenosine monophosphate-activated kinase immunoreactivity was transiently increased in the hippocampal CA1 region 1–2 days after ischemia/reperfusion, while AMPK immunoreactivity was almost undetectable in the stratum pyramidale of the CA1 region 4–7 days after ischemia/reperfusion. The administration of Compound C caused a dose-dependent decrease in the ischemia-induced hyperactive behavior, the depletion of ATP, and lactate accumulation in the hippocampal CA1 region within 24 hours after ischemia/reperfusion. In addition, the administration of Compound C decreased reactive gliosis (astrocytes and microglia) and increased the number of cresyl violet-positive neurons when compared to the vehicle-treated group at 5 days post-ischemia/reperfusion.Conclusion: These results suggest that AMPK is transiently phosphorylated following forebrain ischemia in the hippocampal CA1 region and inhibition of AMPK has neuroprotective effects against ischemic damage through the reduction of ATP depletion and lactate accumulation in the hippocampal CA1 region.

Palmitate induces C-reactive protein expression in human aortic endothelial cells. Relevance to fatty acid–induced endothelial dysfunction

Circulating levels of free fatty acids are commonly elevated in patients with the metabolic syndrome and exert, through activating proinflammatory pathways, harmful effects of the vascular endothelium. In this study, we examined the effect of palmitate (PA) on endothelial C-reactive protein (CRP) expression and the role of CRP in PA-induced nitric oxide (NO) inhibition. Palmitate increased, in a dose-dependent manner, CRP protein expression and production in human aortic endothelial cells (HAECs). Induction of CRP protein was mimicked by ceramide, whereas bromopalmitate and other common free fatty acids such as oleate or linoleate were ineffective. Palmitate also elicited reactive oxygen species production in HAECs, an effect prevented by protein kinase C (PKC) inhibition and adenosine monophosphate–activated kinase (AMPK) activation. Palmitate-treated HAECs showed increased CRP messenger RNA expression and nuclear factor (NF)– κB activation. Induction of CRP expression by PA was prevented by antioxidants and normalized by PKC and mitogen-activated protein kinase inhibitors. Disrupting NF- κB and Janus kinase/signal transducers and activators of transcription pathways or inducing AMPK activation also suppressed the stimulatory effect of PA on CRP messenger RNA expression. Finally, in HAECs, PA reduced NO release, an effect reversed by anti-CRP antibody. These data demonstrate that PA-induced endothelial CRP expression involves PKC-driven oxidative stress, possibly through AMPK inhibition, and activation of downstream redox-sensitive signaling pathways, including NF- κB. They further support a role for endothelial cell–derived CRP as mediator of the suppressive effect of PA on NO production.

Integrating Stress and Growth Signals

To effectively regulate cell growth and proliferation, cells need to interpret signals that serve to measure whether internal and external conditions are favorable--by sensing the presence of growth factors, nutrients, and cellular energy stores--along with signals generated in response to stresses that might prove disruptive to successful proliferation. Many of the latter activate signaling through the tumor suppressor protein p53, whereas growth regulatory pathways feed into activation of the phosphoinositide 3-kinase-related kinase TOR (target of rapamycin). Feng et al. describe experiments that demonstrate cross talk between these two signaling pathways that appears to provide a mechanism to integrate information from the two pathways. In mouse embryo fibroblasts, activation of p53 after stress induced by DNA damage inhibited TOR activity and its downstream effects, and such effects were lost in cells lacking p53. Pharmacological inhibition of AMPK (adenosine monophosphate-activated kinase), the protein kinase that regulates TOR in response to the nutritional status of the cell, indicated that AMPK also mediated the effect of p53 on TOR. Conversely, cells that were deprived of glucose showed phosphorylation of p53 that represents one step in the activation of that protein. The authors suggest that such signaling between nutrient or metabolic pathway and sensors of cellular stress may be necessary to ensure normal cell growth and proliferation. Z. Feng, H. Zhang, A. J. Levine, S. Jin, The coordinate regulation of the p53 and mTOR pathways in cells. Proc. Natl. Acad. Sci. U.S.A. 102 , 8204-8209 (2005). [Abstract] [Full Text]