UHRF1: a novel metabolic guardian restricting AMPK activity

In changing environments, cells modulate resource budgeting through distinct metabolic routes to control growth. Accordingly, the TORC1 and SNF1/AMPK pathways operate contrastingly in nutrient replete or limited environments to maintain homeostasis. The functions of TORC1 under glucose and amino acid limitation are relatively unknown. We identified a modified form of the yeast TORC1 component Kog1/Raptor, which exhibits delayed growth exclusively during glucose and amino acid limitations. Using this, we found a necessary function for Kog1 in these conditions where TORC1 kinase activity is undetectable. Metabolic flux and transcriptome analysis revealed that Kog1 controls SNF1-dependent carbon flux apportioning between glutamate/amino acid biosynthesis and gluconeogenesis. Kog1 regulates SNF1/AMPK activity and outputs and mediates a rapamycin-independent activation of the SNF1 targets Mig1 and Cat8. This enables effective glucose derepression, gluconeogenesis activation, and carbon allocation through different pathways. Therefore, Kog1 centrally regulates metabolic homeostasis and carbon utilization during nutrient limitation by managing SNF1 activity.

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Overexpression of Activated AMPK in the Anopheles stephensi Midgut Impacts Mosquito Metabolism, Reproduction and Plasmodium Resistance

Genes ◽

10.3390/genes12010119 ◽

2021 ◽

Vol 12 (1) ◽

pp. 119

Author(s):

Chioma Oringanje ◽

Lillian R. Delacruz ◽

Yunan Han ◽

Shirley Luckhart ◽

Michael A. Riehle

Keyword(s):

Egg Production ◽

Anopheles Stephensi ◽

Mitochondrial Dynamics ◽

Adult Life ◽

Blood Feeding ◽

Pathogen Resistance ◽

Α Subunit ◽

Significant Difference ◽

Transgenic Lines ◽

Ampk Activity

Mitochondrial integrity and homeostasis in the midgut are key factors controlling mosquito fitness and anti-pathogen resistance. Targeting genes that regulate mitochondrial dynamics represents a potential strategy for limiting mosquito-borne diseases. AMP-activated protein kinase (AMPK) is a key cellular energy sensor found in nearly all eukaryotic cells. When activated, AMPK inhibits anabolic pathways that consume ATP and activates catabolic processes that synthesize ATP. In this study, we overexpressed a truncated and constitutively active α-subunit of AMPK under the control of the midgut-specific carboxypeptidase promotor in the midgut of female Anopheles stephensi. As expected, AMPK overexpression in homozygous transgenic mosquitoes was associated with changes in nutrient storage and metabolism, decreasing glycogen levels at 24 h post-blood feeding when transgene expression was maximal, and concurrently increasing circulating trehalose at the same time point. When transgenic lines were challenged with Plasmodium falciparum, we observed a significant decrease in the prevalence and intensity of infection relative to wild type controls. Surprisingly, we did not observe a significant difference in the survival of adult mosquitoes fed either sugar only or both sugar and bloodmeals throughout adult life. This may be due to the limited period that the transgene was activated before homeostasis was restored. However, we did observe a significant decrease in egg production, suggesting that manipulation of AMPK activity in the mosquito midgut resulted in the re-allocation of resources away from egg production. In summary, this work identifies midgut AMPK activity as an important regulator of metabolism, reproduction, and innate immunity in An. stephensi, a highly invasive and important malaria vector species.

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CD36 promotes NLRP3 inflammasome activation via the mtROS pathway in renal tubular epithelial cells of diabetic kidneys

Cell Death and Disease ◽

10.1038/s41419-021-03813-6 ◽

2021 ◽

Vol 12 (6) ◽

Author(s):

Yanjuan Hou ◽

Qian Wang ◽

Baosheng Han ◽

Yiliang Chen ◽

Xi Qiao ◽

...

Keyword(s):

Nlrp3 Inflammasome ◽

High Glucose ◽

Inflammasome Activation ◽

Ros Production ◽

Tubular Epithelial Cells ◽

Renal Tubular Epithelial Cells ◽

Nlrp3 Inflammasome Activation ◽

Ampk Activity ◽

Renal Tubular ◽

Tubulointerstitial Inflammation

AbstractTubulointerstitial inflammation plays a key role in the pathogenesis of diabetic nephropathy (DN). Interleukin-1β (IL-1β) is the key proinflammatory cytokine associated with tubulointerstitial inflammation. The NLRP3 inflammasome regulates IL-1β activation and secretion. Reactive oxygen species (ROS) represents the main mediator of NLRP3 inflammasome activation. We previously reported that CD36, a class B scavenger receptor, mediates ROS production in DN. Here, we determined whether CD36 is involved in NLRP3 inflammasome activation and explored the underlying mechanisms. We observed that high glucose induced-NLRP3 inflammasome activation mediate IL-1β secretion, caspase-1 activation, and apoptosis in HK-2 cells. In addition, the levels of CD36, NLRP3, and IL-1β expression (protein and mRNA) were all significantly increased under high glucose conditions. CD36 knockdown resulted in decreased NLRP3 activation and IL-1β secretion. CD36 knockdown or the addition of MitoTempo significantly inhibited ROS production in HK-2 cells. CD36 overexpression enhanced NLRP3 activation, which was reduced by MitoTempo. High glucose levels induced a change in the metabolism of HK-2 cells from fatty acid oxidation (FAO) to glycolysis, which promoted mitochondrial ROS (mtROS) production after 72 h. CD36 knockdown increased the level of AMP-activated protein kinase (AMPK) activity and mitochondrial FAO, which was accompanied by the inhibition of NLRP3 and IL-1β. The in vivo experimental results indicate that an inhibition of CD36 could protect diabetic db/db mice from tubulointerstitial inflammation and tubular epithelial cell apoptosis. CD36 mediates mtROS production and NLRP3 inflammasome activation in db/db mice. CD36 inhibition upregulated the level of FAO-related enzymes and AMPK activity in db/db mice. These results suggest that NLRP3 inflammasome activation is mediated by CD36 in renal tubular epithelial cells in DN, which suppresses mitochondrial FAO and stimulates mtROS production.

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

Antioxidants ◽

10.3390/antiox10050776 ◽

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.

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Glucose regulates AMP-activated protein kinase activity and gene expression in clonal, hypothalamic neurons expressing proopiomelanocortin: additive effects of leptin or insulin

Journal of Endocrinology ◽

10.1677/joe-06-0080 ◽

2007 ◽

Vol 192 (3) ◽

pp. 605-614 ◽

Cited By ~ 46

Author(s):

Fang Cai ◽

Armen V Gyulkhandanyan ◽

Michael B Wheeler ◽

Denise D Belsham

Keyword(s):

Protein Kinase ◽

Energy Homeostasis ◽

Cell Model ◽

Neuronal Cell ◽

Cell Types ◽

Glucose Sensing ◽

Protein Kinase Activity ◽

Energy Status ◽

Ampk Activity ◽

Amp Activated Protein Kinase

The mammalian hypothalamus comprises an array of phenotypically distinct cell types that interpret peripheral signals of energy status and, in turn, elicits an appropriate response to maintain energy homeostasis. We used a clonal representative hypothalamic cell model expressing proopiomelanocortin (POMC; N-43/5) to study changes in AMP-activated protein kinase (AMPK) activity and glucose responsiveness. We have demonstrated the presence of cellular machinery responsible for glucose sensing in the cell line, including glucokinase, glucose transporters, and appropriate ion channels. ATP-sensitive potassium channels were functional and responded to glucose. The N-43/5 POMC neurons may therefore be an appropriate cell model to study glucose-sensing mechanisms in the hypothalamus. In N-43/5 POMC neurons, increasing glucose concentrations decreased phospho-AMPK activity. As a relevant downstream effect, we found that POMC transcription increased with 2.8 and 16.7 mM glucose. Upon addition of leptin, with either no glucose or with 5 mM glucose, we found that leptin decreased AMPK activity in N-43/5 POMC neurons, but had no significant effect at 25 mM glucose, whereas insulin decreased AMPK activity at only 5 mM glucose. These results demonstrate that individual hypothalamic neuronal cell types, such as the POMC neuron, can have distinct responses to peripheral signals that relay energy status to the brain, and will therefore be activated uniquely to control neuroendocrine function.

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Adrenaline is a critical mediator of acute exercise-induced AMP-activated protein kinase activation in adipocytes

Biochemical Journal ◽

10.1042/bj20061479 ◽

2007 ◽

Vol 403 (3) ◽

pp. 473-481 ◽

Cited By ~ 81

Author(s):

Ho-Jin Koh ◽

Michael F. Hirshman ◽

Huamei He ◽

Yangfeng Li ◽

Yasuko Manabe ◽

...

Keyword(s):

Protein Kinase ◽

Protein Kinase Activity ◽

Chronic Exercise ◽

Rat Adipocytes ◽

Compound C ◽

Isolated Adipocytes ◽

Ampk Activity ◽

Exercise Induced ◽

Amp Activated Protein Kinase

Exercise increases AMPK (AMP-activated protein kinase) activity in human and rat adipocytes, but the underlying molecular mechanisms and functional consequences of this activation are not known. Since adrenaline (epinephrine) concentrations increase with exercise, in the present study we hypothesized that adrenaline activates AMPK in adipocytes. We show that a single bout of exercise increases AMPKα1 and α2 activities and ACC (acetyl-CoA carboxylase) Ser79 phosphorylation in rat adipocytes. Similarly to exercise, adrenaline treatment in vivo increased AMPK activities and ACC phosphorylation. Pre-treatment of rats with the β-blocker propranolol fully blocked exercise-induced AMPK activation. Increased AMPK activity with exercise and adrenaline treatment in vivo was accompanied by an increased AMP/ATP ratio. Adrenaline incubation of isolated adipocytes also increased the AMP/ATP ratio and AMPK activities, an effect blocked by propranolol. Adrenaline incubation increased lipolysis in isolated adipocytes, and Compound C, an AMPK inhibitor, attenuated this effect. Finally, a potential role for AMPK in the decreased adiposity associated with chronic exercise was suggested by marked increases in AMPKα1 and α2 activities in adipocytes from rats trained for 6 weeks. In conclusion, both acute and chronic exercise are significant regulators of AMPK activity in rat adipocytes. Our findings suggest that adrenaline plays a critical role in exercise-stimulated AMPKα1 and α2 activities in adipocytes, and that AMPK can function in the regulation of lipolysis.

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p-Coumaric Acid Enhances Hypothalamic Leptin Signaling and Glucose Homeostasis in Mice via Differential Effects on AMPK Activation

International Journal of Molecular Sciences ◽

10.3390/ijms22031431 ◽

2021 ◽

Vol 22 (3) ◽

pp. 1431

Author(s):

Linh V. Nguyen ◽

Khoa D. A. Nguyen ◽

Chi-Thanh Ma ◽

Quoc-Thai Nguyen ◽

Huong T. H. Nguyen ◽

...

Keyword(s):

Glucose Homeostasis ◽

Blood Glucose Control ◽

Whole Body ◽

Ampk Activation ◽

Coumaric Acid ◽

Leptin Signaling ◽

Differential Effects ◽

Leptin Sensitivity ◽

Ampk Activity

AMP-activated protein kinase (AMPK) plays a crucial role in the regulation of energy homeostasis in both peripheral metabolic organs and the central nervous system. Recent studies indicated that p-Coumaric acid (CA), a hydroxycinnamic phenolic acid, potentially activated the peripheral AMPK pathway to exert beneficial effects on glucose metabolism in vitro. However, CA’s actions on central AMPK activity and whole-body glucose homeostasis have not yet been investigated. Here, we reported that CA exhibited different effects on peripheral and central AMPK activation both in vitro and in vivo. Specifically, while CA treatment promoted hepatic AMPK activation, it showed an inhibitory effect on hypothalamic AMPK activity possibly by activating the S6 kinase. Furthermore, CA treatment enhanced hypothalamic leptin sensitivity, resulting in increased proopiomelanocortin (POMC) expression, decreased agouti-related peptide (AgRP) expression, and reduced daily food intake. Overall, CA treatment improved blood glucose control, glucose tolerance, and insulin sensitivity. Together, these results suggested that CA treatment enhanced hypothalamic leptin signaling and whole-body glucose homeostasis, possibly via its differential effects on AMPK activation.

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Transthyretin contributes to insulin resistance and diminishes exercise-induced insulin sensitivity in obese mice by inhibiting AMPK activity in skeletal muscle

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00495.2020 ◽

2021 ◽

Author(s):

Yingzi He ◽

Ruojun Qiu ◽

Beibei Wu ◽

Weiwei Gui ◽

Xihua Lin ◽

...

Keyword(s):

Insulin Resistance ◽

Insulin Sensitivity ◽

Inhibitory Effect ◽

Quadriceps Femoris ◽

Treadmill Training ◽

C2c12 Cells ◽

Obese Mice ◽

Insulin Resistant ◽

Ampk Activity ◽

Exercise Induced

Exercise improves obesity-induced insulin resistance and metabolic disorders via mechanisms that remain unclear. Here, we show that the levels of the hepatokine transthyretin (TTR) in circulation are elevated in insulin-resistant individuals including high-fat diet (HFD)-induced obese mice, db/db mice, and patients with metabolic syndrome. Liver Ttr mRNA and circulating TTR levels were reduced in mice by treadmill training, as was the TTR levels in quadriceps femoris muscle; however, AMPK signalling activity was enhanced. Transgenic overexpression of TTR or injection of purified TTR triggered insulin resistance in mice fed on regular chow (RC). Furthermore, TTR overexpression reduced the beneficial effects of exercise on insulin sensitivity in HFD-fed mice. TTR was internalized by muscle cells via the membrane receptor Grp78 and the internalization into the quadriceps femoris was reduced by treadmill training. The TTR/Grp78 combination in C2C12 cells was increased, whereas the AMPK activity of C2C12 cells was decreased as the TTR concentration rose. Additionally, Grp78 silencing prevented the TTR internalization and reversed its inhibitory effect on AMPK activity in C2C12 cells. Our study suggests that elevated circulating TTR may contribute to insulin resistance and counteract the exercise-induced insulin sensitivity improvement; the TTR suppression might be an adaptive response to exercise through enhancing AMPK activity in skeletal muscles.

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