scholarly journals Hyperosmotic Stress Initiates AMPK-Independent Autophagy and AMPK- and Autophagy-Independent Depletion of Thioredoxin 1 and Glyoxalase 2 in HT22 Nerve Cells

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Alcir Luiz Dafre ◽  
Ariana Ern Schmitz ◽  
Pamela Maher
Keyword(s):  
Ribosomal Protein ◽  
Phosphorylation Site ◽  
Nerve Cells ◽  
Hyperosmotic Stress ◽  
Ampk Activation ◽  
Mtor Inhibition ◽  
Ampk Phosphorylation ◽  
Autophagy Induction ◽  
Thioredoxin 1 ◽  
Glyoxalase 2

Background. Hyperosmotic stress is an important pathophysiologic condition in diabetes, severe trauma, dehydration, infection, and ischemia. Furthermore, brain neuronal cells face hyperosmotic stress in ageing and Alzheimer’s disease. Despite the enormous importance of knowing the homeostatic mechanisms underlying the responses of nerve cells to hyperosmotic stress, this topic has been underrepresented in the literature. Recent evidence points to autophagy induction as a hallmark of hyperosmotic stress, which has been proposed to be controlled by mTOR inhibition as a consequence of AMPK activation. We previously showed that methylglyoxal induced a decrease in the antioxidant proteins thioredoxin 1 (Trx1) and glyoxalase 2 (Glo2), which was mediated by AMPK-dependent autophagy. Thus, we hypothesized that hyperosmotic stress would have the same effect. Methods. HT22 hippocampal nerve cells were treated with NaCl (37, 75, or 150 mM), and the activation of the AMPK/mTOR pathway was investigated, as well as the levels of Trx1 and Glo2. To determine if autophagy was involved, the inhibitors bafilomycin (Baf) and chloroquine (CQ), as well as ATG5 siRNA, were used. To test for AMPK involvement, AMPK-deficient mouse embryonic fibroblasts (MEFs) were used. Results. Hyperosmotic stress induced a clear increase in autophagy, which was demonstrated by a decrease in p62 and an increase in LC3 lipidation. AMPK phosphorylation, linked to a decrease in mTOR and S6 ribosomal protein phosphorylation, was also observed. Deletion of AMPK in MEFs did not prevent autophagy induction by hyperosmotic stress, as detected by decreased p62 and increased LC3 II, or mTOR inhibition, inferred by decreased phosphorylation of P70 S6 kinase and S6 ribosomal protein. These data indicating that AMPK was not involved in autophagy activation by hyperosmotic stress were supported by a decrease in pS555-ULK1, an AMPK phosphorylation site. Trx1 and Glo2 levels were decreased at 6 and 18 h after treatment with 150 mM NaCl. However, this decrease in Trx1 and Glo2 in HT22 cells was not prevented by autophagy inhibition by Baf, CQ, or ATG5 siRNA. AMPK-deficient MEFs under hyperosmotic stress presented the same Trx1 and Glo2 decrease as wild-type cells. Conclusion. Hyperosmotic stress induced AMPK activation, but this was not responsible for its effects on mTOR activity or autophagy induction. Moreover, the decrease in Trx1 and Glo2 induced by hyperosmotic stress was independent of both autophagy and AMPK activation.

scholarly journals Apigenin and Luteolin Regulate Autophagy by Targeting NRH-Quinone Oxidoreductase 2 in Liver Cells

Antioxidants ◽  
2021 ◽  
Vol 10 (5) ◽  
pp. 776
Author(s):  
Elzbieta Janda ◽  
Concetta Martino ◽  
Concetta Riillo ◽  
Maddalena Parafati ◽  
Antonella Lascala ◽  
...  
Keyword(s):  
Potential Role ◽  
Autophagic Flux ◽  
Ampk Activation ◽  
Amp Kinase ◽  
Quinone Oxidoreductase ◽  
Ampk Phosphorylation ◽  
Autophagy Induction ◽  
Ampk Activity ◽  
Dietary Flavonoids

Dietary flavonoids stimulate autophagy and prevent liver dysfunction, but the upstream signaling pathways triggered by these compounds are not well understood. Certain polyphenols bind directly to NRH-quinone oxidoreductase 2 (NQO2) and inhibit its activity. NQO2 is highly expressed in the liver, where it participates in quinone metabolism, but recent evidence indicates that it may also play a role in the regulation of oxidative stress and autophagy. Here, we addressed a potential role of NQO2 in autophagy induction by flavonoids. The pro-autophagic activity of seven flavonoid aglycons correlated perfectly with their ability to inhibit NQO2 activity, and flavones such as apigenin and luteolin showed the strongest activity in all assays. The silencing of NQO2 strongly reduced flavone-induced autophagic flux, although it increased basal LC3-II levels in HepG2 cells. Both flavones induced AMP kinase (AMPK) activation, while its reduction by AMPK beta (PRKAB1) silencing inhibited flavone-induced autophagy. Interestingly, the depletion of NQO2 levels by siRNA increased the basal AMPK phosphorylation but abrogated its further increase by apigenin. Thus, NQO2 contributes to the negative regulation of AMPK activity and autophagy, while its targeting by flavones releases pro-autophagic signals. These findings imply that NQO2 works as a flavone receptor mediating autophagy and may contribute to other hepatic effects of flavonoids.

AMPK activation with AICAR provokes an acute fall in plasma [K+]

2008 ◽  
Vol 294 (1) ◽  
pp. C126-C135 ◽  
Author(s):  
Dan Zheng ◽  
Anjana Perianayagam ◽  
Donna H. Lee ◽  
M. Douglas Brannan ◽  
Li E. Yang ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Infusion Rate ◽  
Extracellular Fluid ◽  
Ampk Activation ◽  
Conscious Rats ◽  
Significant Fall ◽  
Ampk Phosphorylation ◽  
Atp Levels ◽  
Ampk Activity ◽  
Amp Activated Protein Kinase

AMP-activated protein kinase (AMPK), activated by an increase in intracellular AMP-to-ATP ratio, stimulates pathways that can restore ATP levels. We tested the hypothesis that AMPK activation influences extracellular fluid (ECF) K+ homeostasis. In conscious rats, AMPK was activated with 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR) infusion: 38.4 mg/kg bolus then 4 mg·kg−1·min−1 infusion. Plasma [K+] and [glucose] both dropped at 1 h of AICAR infusion and [K+] dropped to 3.3 ± 0.04 mM by 3 h, linearly related to the increase in muscle AMPK phosphorylation. AICAR treatment did not increase urinary K+ excretion. AICAR lowered [K+] whether plasma [K+] was chronically elevated or lowered. The K+ infusion rate needed to maintain baseline plasma [K+] reached 15.7 ± 1.3 μmol K+·kg−1·min−1 between 120 and 180 min AICAR infusion. In mice expressing a dominant inhibitory form of AMPK in the muscle (Tg-KD1), baseline [K+] was not different from controls (4.2 ± 0.1 mM), but the fall in plasma [K+] in response to AICAR (0.25 g/kg) was blunted: [K+] fell to 3.6 ± 0.1 in controls and to 3.9 ± 0.1 mM in Tg-KD1, suggesting that ECF K+ redistributes, at least in part, to muscle ICF. In summary, these findings illustrate that activation of AMPK activity with AICAR provokes a significant fall in plasma [K+] and suggest a novel mechanism for redistributing K+ from ECF to ICF.

scholarly journals Regulation of the autophagy protein LC3 by phosphorylation

2010 ◽  
Vol 190 (4) ◽  
pp. 533-539 ◽  
Author(s):  
Salvatore J. Cherra ◽  
Scott M. Kulich ◽  
Guy Uechi ◽  
Manimalha Balasubramani ◽  
John Mountzouris ◽  
...  
Keyword(s):  
Phosphorylation Site ◽  
Carbon Sources ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Leucine Rich Repeat ◽  
Catabolic Pathway ◽  
G2019s Mutation ◽  
Autophagy Induction ◽  
Neuronal Processes ◽  
Pka Catalytic Subunit

Macroautophagy is a major catabolic pathway that impacts cell survival, differentiation, tumorigenesis, and neurodegeneration. Although bulk degradation sustains carbon sources during starvation, autophagy contributes to shrinkage of differentiated neuronal processes. Identification of autophagy-related genes has spurred rapid advances in understanding the recruitment of microtubule-associated protein 1 light chain 3 (LC3) in autophagy induction, although braking mechanisms remain less understood. Using mass spectrometry, we identified a direct protein kinase A (PKA) phosphorylation site on LC3 that regulates its participation in autophagy. Both metabolic (rapamycin) and pathological (MPP+) inducers of autophagy caused dephosphorylation of endogenous LC3. The pseudophosphorylated LC3 mutant showed reduced recruitment to autophagosomes, whereas the nonphosphorylatable mutant exhibited enhanced puncta formation. Finally, autophagy-dependent neurite shortening induced by expression of a Parkinson disease–associated G2019S mutation in leucine-rich repeat kinase 2 was inhibited by dibutyryl–cyclic adenosine monophosphate, cytoplasmic expression of the PKA catalytic subunit, or the LC3 phosphorylation mimic. These data demonstrate a role for phosphorylation in regulating LC3 activity.

Modulation of the anti-tumor activity of VEGF blockade by metformin.

2017 ◽  
Vol 35 (15_suppl) ◽  
pp. e23009-e23009
Author(s):  
Mohamed Selmy ◽  
Elisabetta Zulato ◽  
Anna Pasto ◽  
Stefano Indraccolo
Keyword(s):  
Cell Cycle ◽  
Tumor Growth ◽  
Glucose Deprivation ◽  
Potential Candidate ◽  
Ampk Activation ◽  
Proliferative Capacity ◽  
Combination Strategy ◽  
Mtor Inhibition

e23009 Background: The payoff from first-generation angiogenesis inhibitors was commonly temporary, due to the development of intrinsic as well as acquired resistance. Apart from the vascular resistance due to circumventing VEGF blockade by proangiogenic factors, resistance has also been associated with assortment of resistant clones. Accordingly, a combination strategy was proposed to overcome such resistance. Metformin, as a potential candidate, has received considerable concern as an anticancer agent. Methods: IN-VITRO WORK;Cells were divided into normoxic and hypoxic groups. For both, four subgroups were developed; control, metformin, glucose deprivation and a subgroup in which cells were subjected to both glucose deprivation and metformin treatment. Cells were then subjected to analysis for Apoptosis, Cell cycle progression and western blot. IN-VIVO WORK; Tumor growth was assessed IGROV-1 subcutaneous xenografts. Animal were divided into four groups; control, Metformin, Bevacizumab and a fourth group receiving both drugs. Tumor growth was assessed along treatments and at time of sacrifice.After sacrificing animals, tumors were further analyzed for; necrosis, apoptosis, proliferative capacity, activation of AMPK and its downstream effectors. Results: Our in-vitro results suggested an anti-proliferative effect of metformin in terms of apoptosis, cell cycle arrest, AMPK activation and mTOR inhibition at various time points. In-vivo experiments revealed a significant decrease of tumor weight and proliferative capacity in tumors treated with both drugs and a trend toward a decrease in tumor growth along the treatment. Yet, there was no difference between the bevacizumab and the combination groups regarding AMPK activation suggesting another mechanism to exert the combination effect. The effect of Metformin on CSC percentage and viability was tested. Glucose deprivation plus hypoxia lead to increase in CSC population, while adding metformin to bevacizumab reverse this augmentation in CSC numbers. Conclusions: Study represents a proof of concept study demonstrating a positive modulatory effect of metformin addition to bevacizumab. Additional experimental work on a wider scale is running to ascertain the current results.

scholarly journals Identification of the Serine 307 of LKB1 as a Novel Phosphorylation Site Essential for Its Nucleocytoplasmic Transport and Endothelial Cell Angiogenesis

2009 ◽  
Vol 29 (13) ◽  
pp. 3582-3596 ◽  
Author(s):  
Zhonglin Xie ◽  
Yunzhou Dong ◽  
Junhua Zhang ◽  
Roland Scholz ◽  
Dietbert Neumann ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Nuclear Export ◽  
Consensus Sequence ◽  
Phosphorylation Site ◽  
Muscle Cells ◽  
Nucleocytoplasmic Transport ◽  
Ampk Activation ◽  
Wild Type ◽  
Free System ◽  
Pkc Ζ

ABSTRACT LKB1, a master kinase that controls at least 13 downstream protein kinases including the AMP-activated protein kinase (AMPK), resides mainly in the nucleus. A key step in LKB1 activation is its export from the nucleus to the cytoplasm. Here, we identified S307 of LKB1 as a putative novel phosphorylation site which is essential for its nucleocytoplasmic transport. In a cell-free system, recombinant PKC-ζ phosphorylates LKB1 at S307. AMPK-activating agents stimulate PKC-ζ activity and LKB1 phosphorylation at S307 in endothelial cells, hepatocytes, skeletal muscle cells, and vascular smooth muscle cells. Like the kinase-dead LKB1 D194A mutant (mutation of Asp194 to Ala), the constitutively nucleus-localized LKB1 SL26 mutant and the LKB1 S307A mutant (Ser307 to Ala) exhibit a decreased association with STRADα. Interestingly, the PKC-ζ consensus sequence surrounding LKB1 S307 is disrupted in the LKB1 SL26 mutant, thus providing a likely molecular explanation for this mutation causing LKB1 dysfunction. In addition, LKB1 nucleocytoplasmic transport and AMPK activation in response to peroxynitrite are markedly reduced by pharmacological inhibition of CRM1, which normally facilitates nuclear export of LKB1-STRAD complexes. In comparison to the LKB1 wild type, the S307A mutant complexes show reduced association with CRM1. Finally, adenoviral overexpression of wild-type LKB1 suppresses, while the LKB1 S307A mutant increases, tube formation and hydrogen peroxide-enhanced apoptosis in cultured endothelial cells. Taken together, our results suggest that, in multiple cell types the signaling pathways engaged by several physiological stimuli converge upon PKC-ζ-dependent LKB1 phosphorylation at S307, which directs the nucleocytoplasmic transport of LKB1 and consequent AMPK activation.

scholarly journals Regulation of ERK1/2 by ouabain and Na-K-ATPase-dependent energy utilization and AMPK activation in parotid acinar cells

2008 ◽  
Vol 295 (3) ◽  
pp. C590-C599 ◽  
Author(s):  
Stephen P. Soltoff ◽  
Lee Hedden
Keyword(s):  
Protein Kinase ◽  
Muscarinic Receptor ◽  
Growth Factor Receptor ◽  
Acinar Cells ◽  
Receptor Activation ◽  
Energy Utilization ◽  
Ampk Activation ◽  
Parotid Acinar Cells ◽  
Ampk Phosphorylation ◽  
Rat Parotid

We previously found that the phosphorylation of ERK1/2 by submaximal concentrations of the muscarinic receptor ligand carbachol was potentiated in rat parotid acinar cells exposed to ouabain, a cardiac glycoside that inhibits the Na-K-ATPase. We now report that this signaling phenomenon involves the prevention of negative regulation of extracellular signal-regulated kinase-1/2 (ERK1/2) that is normally mediated by AMP-activated protein kinase (AMPK). Carbachol increases the turnover of the ATP-consuming Na-K-ATPase, reducing intracellular ATP and promoting the phosphorylation/activation of the energy sensor AMPK. Ouabain blocks the reduction in ATP and subsequent AMPK phosphorylation, which is regulated by the AMP-to-ATP ratio. The ouabain-promoted enhancement of ERK1/2 phosphorylation was not reproduced in Par-C10 cells, an immortalized rat parotid cell line that did not respond to carbachol with an ATP reduction and that employs an upstream AMPK kinase (Ca2+/calmodulin-dependent protein kinase kinase, CaMKK) different from that (LKB1) in native cells. In native parotid cells, inhibitory effects of AMPK on ERK1/2 signaling were examined by activating AMPK with 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR), which is converted to an AMP mimetic but does not alter parotid ATP levels. AICAR-treated cells display increases in AMPK phosphorylation and a reduced phosphorylation of ERK1/2 subsequent to activation of muscarinic and P2X7 receptors, which promote increases in Na-K-ATPase turnover, but not upon epidermal growth factor receptor activation. These results suggest that carbachol-initiated AMPK activation can produce a negative feedback on ERK1/2 signaling in response to submaximal muscarinic receptor activation and that increases in fluid secretion can modulate receptor-initiated signaling events indirectly by producing ion transport-dependent decreases in ATP.

scholarly journals ANTI-DIABETIC EFFECTS OF GLUCOMANNO-OLIGOSACCHARIDES VIA AMPK ACTIVATION IN C2C12 MYOTUBES

2021 ◽  
Vol 59 (4) ◽  
pp. 467
Author(s):  
Thien Truong Do ◽  
Nu Thi Tran ◽  
Que Nguyet Thi Do ◽  
Nhi Thi Y Tran
Keyword(s):  
C2c12 Myotubes ◽  
Control Group ◽  
Ampk Activation ◽  
Independent Manner ◽  
Glucose Levels ◽  
Blood Glucose Levels ◽  
Ampk Phosphorylation ◽  
Amp Activated Protein Kinase

Abstract-HCTN7. In this paper, antidiabetic activities of glucomanno-oligosaccharides (GMO) in vitro and in vivo were investigated. GMO significantly increased AMP-activated protein kinase (AMPK) phosphorylation in a concentration-independent manner. Treatment with 100μg/ml and 50μg/ml of GMO for 1 hour caused 1.47-fold and 1.81-fold phosphorylation of AMPK, respectively. Oral administration of GMO (6g/kg-1 of body weight day-1) lowered blood glucose levels (p < 0.05) at 120 min as compared to control group. These results suggested that GMO exhibited anti-diabetic effects via activation of AMPK and could be useful for diabetes prevention

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